diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index f61aa3ab900eb..862e43748d705 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -2266,8 +2266,13 @@ namespace ts {
         }
 
         function checkStrictModeNumericLiteral(node: NumericLiteral) {
-            if (inStrictMode && node.numericLiteralFlags & TokenFlags.Octal) {
-                file.bindDiagnostics.push(createDiagnosticForNode(node, Diagnostics.Octal_literals_are_not_allowed_in_strict_mode));
+            if (inStrictMode) {
+                if (node.numericLiteralFlags & TokenFlags.Octal) {
+                    file.bindDiagnostics.push(createDiagnosticForNode(node, Diagnostics.Octal_literals_are_not_allowed_in_strict_mode));
+                }
+                else if (node.numericLiteralFlags & TokenFlags.StartsWithZero) {
+                    file.bindDiagnostics.push(createDiagnosticForNode(node, Diagnostics.Number_literals_starting_with_0_are_not_allowed_in_strict_mode));
+                }
             }
         }
 
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index d0d66f0f959b8..d9250e34cf16c 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1180,6 +1180,14 @@
         "category": "Error",
         "code": 1388
     },
+    "Number literals starting with '0' are not allowed in strict mode.": {
+        "category": "Error",
+        "code": 1389
+    },
+    "A bigint literal cannot start with '0'.": {
+        "category": "Error",
+        "code": 1390
+    },
 
     "The types of '{0}' are incompatible between these types.": {
         "category": "Error",
@@ -4677,6 +4685,10 @@
         "category": "Error",
         "code": 6504
     },
+    "Numeric separators are not allowed in numbers that start with '0'.": {
+        "category": "Error",
+        "code": 6505
+    },
 
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
diff --git a/src/compiler/scanner.ts b/src/compiler/scanner.ts
index 77ec82ffef760..f34e5e37176eb 100644
--- a/src/compiler/scanner.ts
+++ b/src/compiler/scanner.ts
@@ -1094,6 +1094,116 @@ namespace ts {
             }
         }
 
+        function scanPotentiallyOctalNumberFragment(): { fragment: string, isOctalCandidate: boolean } {
+            let start = pos;
+            let allowSeparator = false;
+            let isPreviousTokenSeparator = false;
+            let shouldShowLeadingZeroError = true;
+            let isOctalCandidate = pos + 1 < end && isOctalDigit(text.charCodeAt(pos + 1));
+            let result = "";
+            while (true) {
+                const ch = text.charCodeAt(pos);
+                if (ch === CharacterCodes._) {
+                    tokenFlags |= TokenFlags.ContainsSeparator;
+                    isOctalCandidate = false;
+                    if (allowSeparator) {
+                        allowSeparator = false;
+                        isPreviousTokenSeparator = true;
+                        result += text.substring(start, pos);
+                    }
+                    else if (isPreviousTokenSeparator) {
+                        error(Diagnostics.Multiple_consecutive_numeric_separators_are_not_permitted, pos, 1);
+                    }
+                    else {
+                        error(Diagnostics.Numeric_separators_are_not_allowed_here, pos, 1);
+                    }
+                    if (shouldShowLeadingZeroError) {
+                        error(Diagnostics.Numeric_separators_are_not_allowed_in_numbers_that_start_with_0, pos, 1);
+                        shouldShowLeadingZeroError = false;
+                    }
+                    pos++;
+                    start = pos;
+                    continue;
+                }
+                if (isDigit(ch)) {
+                    if (!isOctalDigit(ch)) {
+                        isOctalCandidate = false;
+                    }
+                    allowSeparator = true;
+                    isPreviousTokenSeparator = false;
+                    pos++;
+                    continue;
+                }
+                break;
+            }
+            if (text.charCodeAt(pos - 1) === CharacterCodes._) {
+                error(Diagnostics.Numeric_separators_are_not_allowed_here, pos - 1, 1);
+            }
+            return { fragment: result + text.substring(start, pos), isOctalCandidate };
+        }
+
+        function scanZeroLeadingNumber(): { type: SyntaxKind, value: string } {
+            const start = pos;
+            const { fragment: mainFragment, isOctalCandidate } = scanPotentiallyOctalNumberFragment();
+            let decimalFragment: string | undefined;
+            let scientificFragment: string | undefined;
+            if (text.charCodeAt(pos) === CharacterCodes.dot && !(isOctalCandidate && isIdentifierStart(codePointAt(text, pos + 1), languageVersion))) {
+                pos++;
+                decimalFragment = scanNumberFragment();
+            }
+            let end = pos;
+            if (text.charCodeAt(pos) === CharacterCodes.E || text.charCodeAt(pos) === CharacterCodes.e) {
+                pos++;
+                tokenFlags |= TokenFlags.Scientific;
+                if (text.charCodeAt(pos) === CharacterCodes.plus || text.charCodeAt(pos) === CharacterCodes.minus) pos++;
+                const preNumericPart = pos;
+                const finalFragment = scanNumberFragment();
+                if (!finalFragment) {
+                    error(Diagnostics.Digit_expected);
+                }
+                else {
+                    scientificFragment = text.substring(end, preNumericPart) + finalFragment;
+                    end = pos;
+                }
+            }
+            let result: string;
+            if (tokenFlags & TokenFlags.ContainsSeparator) {
+                result = mainFragment;
+                if (decimalFragment) {
+                    result += "." + decimalFragment;
+                }
+                if (scientificFragment) {
+                    result += scientificFragment;
+                }
+            }
+            else {
+                result = text.substring(start, end); // No need to use all the fragments; no _ removal needed
+            }
+
+            if (decimalFragment !== undefined || tokenFlags & TokenFlags.Scientific) {
+                checkForIdentifierStartAfterNumericLiteral(start, decimalFragment === undefined && !!(tokenFlags & TokenFlags.Scientific));
+                return {
+                    type: SyntaxKind.NumericLiteral,
+                    value: "" + +result // if value is not an integer, it can be safely coerced to a number
+                };
+            }
+            else {
+                let type = SyntaxKind.NumericLiteral;
+                tokenValue = "" + +result;
+                if (text.charCodeAt(pos) === CharacterCodes.n) {
+                    type = SyntaxKind.BigIntLiteral;
+                    tokenValue = parsePseudoBigInt(tokenValue + "n") + "n";
+                    pos++;
+                    error(Diagnostics.A_bigint_literal_cannot_start_with_0, start, pos - start);
+                }
+                else if (isOctalCandidate) {
+                    tokenFlags |= TokenFlags.Octal;
+                }
+                checkForIdentifierStartAfterNumericLiteral(start);
+                return { type, value: tokenValue };
+            }
+        }
+
         function checkForIdentifierStartAfterNumericLiteral(numericStart: number, isScientific?: boolean) {
             if (!isIdentifierStart(codePointAt(text, pos), languageVersion)) {
                 return;
@@ -1116,14 +1226,6 @@ namespace ts {
             }
         }
 
-        function scanOctalDigits(): number {
-            const start = pos;
-            while (isOctalDigit(text.charCodeAt(pos))) {
-                pos++;
-            }
-            return +(text.substring(start, pos));
-        }
-
         /**
          * Scans the given number of hexadecimal digits in the text,
          * returning -1 if the given number is unavailable.
@@ -1852,16 +1954,13 @@ namespace ts {
                             tokenFlags |= TokenFlags.OctalSpecifier;
                             return token = checkBigIntSuffix();
                         }
-                        // Try to parse as an octal
-                        if (pos + 1 < end && isOctalDigit(text.charCodeAt(pos + 1))) {
-                            tokenValue = "" + scanOctalDigits();
-                            tokenFlags |= TokenFlags.Octal;
-                            return token = SyntaxKind.NumericLiteral;
+                        else if (pos + 1 < end && (isDigit(text.charCodeAt(pos + 1)) || text.charCodeAt(pos + 1) === CharacterCodes._)) {
+                            tokenFlags |= TokenFlags.StartsWithZero;
+                            ({ type: token, value: tokenValue } = scanZeroLeadingNumber());
+                            return token;
                         }
-                    // This fall-through is a deviation from the EcmaScript grammar. The grammar says that a leading zero
-                    // can only be followed by an octal digit, a dot, or the end of the number literal. However, we are being
-                    // permissive and allowing decimal digits of the form 08* and 09* (which many browsers also do).
-                    // falls through
+
+                    // Fallthrough only for single digit number '0' or number starting with '0.' which don't need special checks
                     case CharacterCodes._1:
                     case CharacterCodes._2:
                     case CharacterCodes._3:
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 0db378efd7b36..ef372077f0945 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -2078,9 +2078,11 @@ namespace ts {
         /* @internal */
         ContainsInvalidEscape = 1 << 11,    // e.g. `\uhello`
         /* @internal */
+        StartsWithZero = 1 << 12,
+        /* @internal */
         BinaryOrOctalSpecifier = BinarySpecifier | OctalSpecifier,
         /* @internal */
-        NumericLiteralFlags = Scientific | Octal | HexSpecifier | BinaryOrOctalSpecifier | ContainsSeparator,
+        NumericLiteralFlags = Scientific | Octal | HexSpecifier | BinaryOrOctalSpecifier | ContainsSeparator | StartsWithZero,
         /* @internal */
         TemplateLiteralLikeFlags = ContainsInvalidEscape,
     }
diff --git a/tests/baselines/reference/jsFileCompilationBindStrictModeErrors.errors.txt b/tests/baselines/reference/jsFileCompilationBindStrictModeErrors.errors.txt
index f2d68282c67fd..011d66dd62c19 100644
--- a/tests/baselines/reference/jsFileCompilationBindStrictModeErrors.errors.txt
+++ b/tests/baselines/reference/jsFileCompilationBindStrictModeErrors.errors.txt
@@ -11,8 +11,7 @@ tests/cases/compiler/b.js(3,7): error TS1210: Invalid use of 'eval'. Class defin
 tests/cases/compiler/b.js(6,13): error TS1213: Identifier expected. 'let' is a reserved word in strict mode. Class definitions are automatically in strict mode.
 tests/cases/compiler/c.js(1,12): error TS1214: Identifier expected. 'let' is a reserved word in strict mode. Modules are automatically in strict mode.
 tests/cases/compiler/c.js(2,5): error TS1215: Invalid use of 'eval'. Modules are automatically in strict mode.
-tests/cases/compiler/d.js(2,9): error TS1121: Octal literals are not allowed in strict mode.
-tests/cases/compiler/d.js(2,11): error TS1005: ',' expected.
+tests/cases/compiler/d.js(2,9): error TS1389: Number literals starting with '0' are not allowed in strict mode.
 
 
 ==== tests/cases/compiler/a.js (9 errors) ====
@@ -75,10 +74,8 @@ tests/cases/compiler/d.js(2,11): error TS1005: ',' expected.
 !!! error TS1215: Invalid use of 'eval'. Modules are automatically in strict mode.
     };
     
-==== tests/cases/compiler/d.js (2 errors) ====
+==== tests/cases/compiler/d.js (1 errors) ====
     "use strict";
     var x = 009; // error
-            ~~
-!!! error TS1121: Octal literals are not allowed in strict mode.
-              ~
-!!! error TS1005: ',' expected.
\ No newline at end of file
+            ~~~
+!!! error TS1389: Number literals starting with '0' are not allowed in strict mode.
\ No newline at end of file
diff --git a/tests/baselines/reference/jsFileCompilationBindStrictModeErrors.types b/tests/baselines/reference/jsFileCompilationBindStrictModeErrors.types
index 4f59172ff9ace..814df00a7fc33 100644
--- a/tests/baselines/reference/jsFileCompilationBindStrictModeErrors.types
+++ b/tests/baselines/reference/jsFileCompilationBindStrictModeErrors.types
@@ -79,6 +79,5 @@ var eval = function () {
 
 var x = 009; // error
 >x : number
->00 : 0
->9 : 9
+>009 : 9
 
diff --git a/tests/baselines/reference/parseBigInt.errors.txt b/tests/baselines/reference/parseBigInt.errors.txt
index 4641e88f13774..6c1782db7007e 100644
--- a/tests/baselines/reference/parseBigInt.errors.txt
+++ b/tests/baselines/reference/parseBigInt.errors.txt
@@ -1,6 +1,6 @@
 tests/cases/compiler/parseBigInt.ts(51,20): error TS2736: Operator '+' cannot be applied to type 'bigint'.
 tests/cases/compiler/parseBigInt.ts(52,23): error TS2736: Operator '+' cannot be applied to type 'bigint'.
-tests/cases/compiler/parseBigInt.ts(56,25): error TS1005: ',' expected.
+tests/cases/compiler/parseBigInt.ts(56,21): error TS1390: A bigint literal cannot start with '0'.
 tests/cases/compiler/parseBigInt.ts(57,22): error TS1352: A bigint literal cannot use exponential notation.
 tests/cases/compiler/parseBigInt.ts(58,19): error TS1353: A bigint literal must be an integer.
 tests/cases/compiler/parseBigInt.ts(59,26): error TS1353: A bigint literal must be an integer.
@@ -78,8 +78,8 @@ tests/cases/compiler/parseBigInt.ts(70,72): error TS2345: Argument of type '3' i
     // Parsing errors
     // In separate blocks because they each declare an "n" variable
     { const legacyOct = 0123n; }
-                            ~
-!!! error TS1005: ',' expected.
+                        ~~~~~
+!!! error TS1390: A bigint literal cannot start with '0'.
     { const scientific = 1e2n; }
                          ~~~~
 !!! error TS1352: A bigint literal cannot use exponential notation.
diff --git a/tests/baselines/reference/parseBigInt.js b/tests/baselines/reference/parseBigInt.js
index 1ffccb11e64fe..c8cb855d50400 100644
--- a/tests/baselines/reference/parseBigInt.js
+++ b/tests/baselines/reference/parseBigInt.js
@@ -120,7 +120,7 @@ const unaryPlusHex = +0x123n;
 // Parsing errors
 // In separate blocks because they each declare an "n" variable
 {
-    const legacyOct = 0123, n;
+    const legacyOct = 123n;
 }
 {
     const scientific = 1e2n;
diff --git a/tests/baselines/reference/parseBigInt.symbols b/tests/baselines/reference/parseBigInt.symbols
index 89ce1a8173ba5..0b1cb8ae608e1 100644
--- a/tests/baselines/reference/parseBigInt.symbols
+++ b/tests/baselines/reference/parseBigInt.symbols
@@ -127,7 +127,6 @@ const unaryPlusHex = +0x123n;
 // In separate blocks because they each declare an "n" variable
 { const legacyOct = 0123n; }
 >legacyOct : Symbol(legacyOct, Decl(parseBigInt.ts, 55, 7))
->n : Symbol(n, Decl(parseBigInt.ts, 55, 24))
 
 { const scientific = 1e2n; }
 >scientific : Symbol(scientific, Decl(parseBigInt.ts, 56, 7))
diff --git a/tests/baselines/reference/parseBigInt.types b/tests/baselines/reference/parseBigInt.types
index 70fd3fa3a600a..a29555c303200 100644
--- a/tests/baselines/reference/parseBigInt.types
+++ b/tests/baselines/reference/parseBigInt.types
@@ -174,9 +174,8 @@ const unaryPlusHex = +0x123n;
 // Parsing errors
 // In separate blocks because they each declare an "n" variable
 { const legacyOct = 0123n; }
->legacyOct : 123
->0123 : 123
->n : any
+>legacyOct : 123n
+>0123n : 123n
 
 { const scientific = 1e2n; }
 >scientific : 100
diff --git a/tests/baselines/reference/parser.numericSeparators.binaryNegative.errors.txt b/tests/baselines/reference/parser.numericSeparators.binaryNegative.errors.txt
index 93118bc9c7fb7..ebbb90c3281d0 100644
--- a/tests/baselines/reference/parser.numericSeparators.binaryNegative.errors.txt
+++ b/tests/baselines/reference/parser.numericSeparators.binaryNegative.errors.txt
@@ -1,6 +1,6 @@
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/1.ts(1,5): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/2.ts(1,3): error TS6188: Numeric separators are not allowed here.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,3): error TS1351: An identifier or keyword cannot immediately follow a numeric literal.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,3): error TS2304: Cannot find name 'B0101'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/4.ts(1,6): error TS6189: Multiple consecutive numeric separators are not permitted.
@@ -23,7 +23,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/6.ts(1,5): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts (3 errors) ====
     0_B0101
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
       ~~~~~
 !!! error TS1351: An identifier or keyword cannot immediately follow a numeric literal.
       ~~~~~
diff --git a/tests/baselines/reference/parser.numericSeparators.decmialNegative.errors.txt b/tests/baselines/reference/parser.numericSeparators.decmialNegative.errors.txt
index 8e48e7c1750e6..b84f2ff6c32a9 100644
--- a/tests/baselines/reference/parser.numericSeparators.decmialNegative.errors.txt
+++ b/tests/baselines/reference/parser.numericSeparators.decmialNegative.errors.txt
@@ -1,22 +1,23 @@
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/1.ts(1,1): error TS2304: Cannot find name '_10'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/10.ts(1,4): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/11.ts(1,5): error TS6189: Multiple consecutive numeric separators are not permitted.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/12.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/12.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/13.ts(1,3): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/14.ts(1,4): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/15.ts(1,5): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/16.ts(1,1): error TS2304: Cannot find name '_0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/16.ts(1,3): error TS1005: ';' expected.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/17.ts(1,6): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/18.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/18.ts(1,3): error TS6189: Multiple consecutive numeric separators are not permitted.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/19.ts(1,5): error TS6189: Multiple consecutive numeric separators are not permitted.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/2.ts(1,3): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/20.ts(1,8): error TS6189: Multiple consecutive numeric separators are not permitted.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/21.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/21.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/22.ts(1,4): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/23.ts(1,5): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/24.ts(1,6): error TS6189: Multiple consecutive numeric separators are not permitted.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/25.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/25.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/26.ts(1,3): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/27.ts(1,4): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/28.ts(1,6): error TS6188: Numeric separators are not allowed here.
@@ -24,21 +25,23 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/29.ts(1,1): erro
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/29.ts(1,3): error TS1005: ';' expected.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,3): error TS6189: Multiple consecutive numeric separators are not permitted.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/30.ts(1,7): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/31.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/31.ts(1,3): error TS6189: Multiple consecutive numeric separators are not permitted.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/32.ts(1,5): error TS6189: Multiple consecutive numeric separators are not permitted.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/33.ts(1,9): error TS6189: Multiple consecutive numeric separators are not permitted.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/34.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/34.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/35.ts(1,4): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/36.ts(1,5): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/37.ts(1,6): error TS6189: Multiple consecutive numeric separators are not permitted.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/38.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/38.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/39.ts(1,3): error TS6188: Numeric separators are not allowed here.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/4.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/4.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/40.ts(1,4): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/41.ts(1,6): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/42.ts(1,1): error TS2304: Cannot find name '_0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/42.ts(1,3): error TS1005: ';' expected.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/43.ts(1,7): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/44.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/44.ts(1,3): error TS6189: Multiple consecutive numeric separators are not permitted.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/45.ts(1,5): error TS6189: Multiple consecutive numeric separators are not permitted.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/46.ts(1,9): error TS6189: Multiple consecutive numeric separators are not permitted.
@@ -52,9 +55,11 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/5.ts(1,3): error
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/50.ts(1,5): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/50.ts(1,6): error TS1124: Digit expected.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/51.ts(1,3): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/52.ts(1,3): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/53.ts(1,3): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/6.ts(1,5): error TS6189: Multiple consecutive numeric separators are not permitted.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/7.ts(1,5): error TS6189: Multiple consecutive numeric separators are not permitted.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/8.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/8.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error TS6188: Numeric separators are not allowed here.
 
 
@@ -76,7 +81,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/4.ts (1 errors) ====
     0_.0
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
     
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/5.ts (1 errors) ====
     0._0
@@ -96,7 +101,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/8.ts (1 errors) ====
     0_e0
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
     
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts (1 errors) ====
     0e_0
@@ -116,7 +121,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/12.ts (1 errors) ====
     0_.0e0
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
     
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/13.ts (1 errors) ====
     0._0e0
@@ -145,8 +150,10 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
          ~
 !!! error TS6188: Numeric separators are not allowed here.
     
-==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/18.ts (1 errors) ====
+==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/18.ts (2 errors) ====
     0__0.0e0
+     ~
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
       ~
 !!! error TS6189: Multiple consecutive numeric separators are not permitted.
     
@@ -163,7 +170,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/21.ts (1 errors) ====
     0_e+0
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
     
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/22.ts (1 errors) ====
     0e+_0
@@ -183,7 +190,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/25.ts (1 errors) ====
     0_.0e+0
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
     
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/26.ts (1 errors) ====
     0._0e+0
@@ -212,8 +219,10 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
           ~
 !!! error TS6188: Numeric separators are not allowed here.
     
-==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/31.ts (1 errors) ====
+==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/31.ts (2 errors) ====
     0__0.0e+0
+     ~
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
       ~
 !!! error TS6189: Multiple consecutive numeric separators are not permitted.
     
@@ -230,7 +239,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/34.ts (1 errors) ====
     0_e+0
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
     
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/35.ts (1 errors) ====
     0e-_0
@@ -250,7 +259,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/38.ts (1 errors) ====
     0_.0e-0
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
     
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/39.ts (1 errors) ====
     0._0e-0
@@ -279,8 +288,10 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
           ~
 !!! error TS6188: Numeric separators are not allowed here.
     
-==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/44.ts (1 errors) ====
+==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/44.ts (2 errors) ====
     0__0.0e-0
+     ~
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
       ~
 !!! error TS6189: Multiple consecutive numeric separators are not permitted.
     
@@ -326,4 +337,14 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/9.ts(1,3): error
     0._
       ~
 !!! error TS6188: Numeric separators are not allowed here.
+    
+==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/52.ts (1 errors) ====
+    09_0
+      ~
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
+    
+==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/53.ts (1 errors) ====
+    07_0
+      ~
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/parser.numericSeparators.decmialNegative.js b/tests/baselines/reference/parser.numericSeparators.decmialNegative.js
index 2ccffcc146067..c7d7c8b649cca 100644
--- a/tests/baselines/reference/parser.numericSeparators.decmialNegative.js
+++ b/tests/baselines/reference/parser.numericSeparators.decmialNegative.js
@@ -153,6 +153,12 @@ _0.0e-0
 //// [51.ts]
 0._
 
+//// [52.ts]
+09_0
+
+//// [53.ts]
+07_0
+
 
 //// [1.js]
 _10;
@@ -260,3 +266,7 @@ _;
 1 - 10;
 //// [51.js]
 0;
+//// [52.js]
+90;
+//// [53.js]
+70;
diff --git a/tests/baselines/reference/parser.numericSeparators.decmialNegative.symbols b/tests/baselines/reference/parser.numericSeparators.decmialNegative.symbols
index daa418358b988..2cee977ce0be1 100644
--- a/tests/baselines/reference/parser.numericSeparators.decmialNegative.symbols
+++ b/tests/baselines/reference/parser.numericSeparators.decmialNegative.symbols
@@ -151,4 +151,10 @@ No type information for this code.
 No type information for this code.=== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/51.ts ===
 0._
 No type information for this code.
+No type information for this code.=== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/52.ts ===
+09_0
+No type information for this code.
+No type information for this code.=== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/53.ts ===
+07_0
+No type information for this code.
 No type information for this code.
\ No newline at end of file
diff --git a/tests/baselines/reference/parser.numericSeparators.decmialNegative.types b/tests/baselines/reference/parser.numericSeparators.decmialNegative.types
index 84ab9b585b90e..ccd94f949ee36 100644
--- a/tests/baselines/reference/parser.numericSeparators.decmialNegative.types
+++ b/tests/baselines/reference/parser.numericSeparators.decmialNegative.types
@@ -210,3 +210,11 @@ _0.0e-0
 0._
 >0._ : 0
 
+=== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/52.ts ===
+09_0
+>09_0 : 90
+
+=== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/53.ts ===
+07_0
+>07_0 : 70
+
diff --git a/tests/baselines/reference/parser.numericSeparators.hexNegative.errors.txt b/tests/baselines/reference/parser.numericSeparators.hexNegative.errors.txt
index c6048a1bbfb4c..2638591aeeae8 100644
--- a/tests/baselines/reference/parser.numericSeparators.hexNegative.errors.txt
+++ b/tests/baselines/reference/parser.numericSeparators.hexNegative.errors.txt
@@ -1,6 +1,6 @@
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/1.ts(1,5): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/2.ts(1,3): error TS6188: Numeric separators are not allowed here.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,3): error TS1351: An identifier or keyword cannot immediately follow a numeric literal.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,3): error TS2304: Cannot find name 'X0101'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/4.ts(1,6): error TS6189: Multiple consecutive numeric separators are not permitted.
@@ -23,7 +23,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/6.ts(1,5): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts (3 errors) ====
     0_X0101
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
       ~~~~~
 !!! error TS1351: An identifier or keyword cannot immediately follow a numeric literal.
       ~~~~~
diff --git a/tests/baselines/reference/parser.numericSeparators.octalNegative.errors.txt b/tests/baselines/reference/parser.numericSeparators.octalNegative.errors.txt
index ebdec3371aa64..74ea2a8143718 100644
--- a/tests/baselines/reference/parser.numericSeparators.octalNegative.errors.txt
+++ b/tests/baselines/reference/parser.numericSeparators.octalNegative.errors.txt
@@ -1,6 +1,6 @@
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/1.ts(1,5): error TS6188: Numeric separators are not allowed here.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/2.ts(1,3): error TS6188: Numeric separators are not allowed here.
-tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,2): error TS6188: Numeric separators are not allowed here.
+tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,2): error TS6505: Numeric separators are not allowed in numbers that start with '0'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,3): error TS1351: An identifier or keyword cannot immediately follow a numeric literal.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts(1,3): error TS2304: Cannot find name 'O0101'.
 tests/cases/conformance/parser/ecmascriptnext/numericSeparators/4.ts(1,6): error TS6189: Multiple consecutive numeric separators are not permitted.
@@ -23,7 +23,7 @@ tests/cases/conformance/parser/ecmascriptnext/numericSeparators/6.ts(1,5): error
 ==== tests/cases/conformance/parser/ecmascriptnext/numericSeparators/3.ts (3 errors) ====
     0_O0101
      ~
-!!! error TS6188: Numeric separators are not allowed here.
+!!! error TS6505: Numeric separators are not allowed in numbers that start with '0'.
       ~~~~~
 !!! error TS1351: An identifier or keyword cannot immediately follow a numeric literal.
       ~~~~~
diff --git a/tests/baselines/reference/scannerES3NumericLiteral3.errors.txt b/tests/baselines/reference/scannerES3NumericLiteral3.errors.txt
deleted file mode 100644
index 51df5a9c33c3f..0000000000000
--- a/tests/baselines/reference/scannerES3NumericLiteral3.errors.txt
+++ /dev/null
@@ -1,7 +0,0 @@
-tests/cases/conformance/scanner/ecmascript3/scannerES3NumericLiteral3.ts(1,3): error TS1005: ';' expected.
-
-
-==== tests/cases/conformance/scanner/ecmascript3/scannerES3NumericLiteral3.ts (1 errors) ====
-    01.0
-      ~~
-!!! error TS1005: ';' expected.
\ No newline at end of file
diff --git a/tests/baselines/reference/scannerES3NumericLiteral3.js b/tests/baselines/reference/scannerES3NumericLiteral3.js
index 544953a1134ac..7ecb6c8d37747 100644
--- a/tests/baselines/reference/scannerES3NumericLiteral3.js
+++ b/tests/baselines/reference/scannerES3NumericLiteral3.js
@@ -2,5 +2,4 @@
 01.0
 
 //// [scannerES3NumericLiteral3.js]
-01;
-.0;
+01.0;
diff --git a/tests/baselines/reference/scannerES3NumericLiteral3.types b/tests/baselines/reference/scannerES3NumericLiteral3.types
index 686e1857bfa05..a300561b59d8b 100644
--- a/tests/baselines/reference/scannerES3NumericLiteral3.types
+++ b/tests/baselines/reference/scannerES3NumericLiteral3.types
@@ -1,5 +1,4 @@
 === tests/cases/conformance/scanner/ecmascript3/scannerES3NumericLiteral3.ts ===
 01.0
->01 : 1
->.0 : 0
+>01.0 : 1
 
diff --git a/tests/baselines/reference/scannerNumericLiteral3.errors.txt b/tests/baselines/reference/scannerNumericLiteral3.errors.txt
deleted file mode 100644
index 894eb391f6043..0000000000000
--- a/tests/baselines/reference/scannerNumericLiteral3.errors.txt
+++ /dev/null
@@ -1,7 +0,0 @@
-tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral3.ts(1,3): error TS1005: ';' expected.
-
-
-==== tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral3.ts (1 errors) ====
-    01.0
-      ~~
-!!! error TS1005: ';' expected.
\ No newline at end of file
diff --git a/tests/baselines/reference/scannerNumericLiteral3.js b/tests/baselines/reference/scannerNumericLiteral3.js
index 8e751bbd841b7..382c0622ac22f 100644
--- a/tests/baselines/reference/scannerNumericLiteral3.js
+++ b/tests/baselines/reference/scannerNumericLiteral3.js
@@ -2,5 +2,4 @@
 01.0
 
 //// [scannerNumericLiteral3.js]
-01;
-.0;
+01.0;
diff --git a/tests/baselines/reference/scannerNumericLiteral3.types b/tests/baselines/reference/scannerNumericLiteral3.types
index 0c175db8fb2ab..be53faca7abf9 100644
--- a/tests/baselines/reference/scannerNumericLiteral3.types
+++ b/tests/baselines/reference/scannerNumericLiteral3.types
@@ -1,5 +1,4 @@
 === tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral3.ts ===
 01.0
->01 : 1
->.0 : 0
+>01.0 : 1
 
diff --git a/tests/baselines/reference/scannerNumericLiteral9.errors.txt b/tests/baselines/reference/scannerNumericLiteral9.errors.txt
deleted file mode 100644
index 7f53ca111d981..0000000000000
--- a/tests/baselines/reference/scannerNumericLiteral9.errors.txt
+++ /dev/null
@@ -1,7 +0,0 @@
-tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral9.ts(1,3): error TS1005: ';' expected.
-
-
-==== tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral9.ts (1 errors) ====
-    009
-      ~
-!!! error TS1005: ';' expected.
\ No newline at end of file
diff --git a/tests/baselines/reference/scannerNumericLiteral9.js b/tests/baselines/reference/scannerNumericLiteral9.js
index a391606ecdf91..bf650744ecfdc 100644
--- a/tests/baselines/reference/scannerNumericLiteral9.js
+++ b/tests/baselines/reference/scannerNumericLiteral9.js
@@ -2,5 +2,4 @@
 009
 
 //// [scannerNumericLiteral9.js]
-00;
-9;
+009;
diff --git a/tests/baselines/reference/scannerNumericLiteral9.types b/tests/baselines/reference/scannerNumericLiteral9.types
index f204fa0977fc2..95bb891139f0b 100644
--- a/tests/baselines/reference/scannerNumericLiteral9.types
+++ b/tests/baselines/reference/scannerNumericLiteral9.types
@@ -1,5 +1,4 @@
 === tests/cases/conformance/scanner/ecmascript5/scannerNumericLiteral9.ts ===
 009
->00 : 0
->9 : 9
+>009 : 9
 
diff --git a/tests/cases/conformance/parser/ecmascriptnext/numericSeparators/parser.numericSeparators.decmialNegative.ts b/tests/cases/conformance/parser/ecmascriptnext/numericSeparators/parser.numericSeparators.decmialNegative.ts
index 3c294148c19e7..c55041c24b6da 100644
--- a/tests/cases/conformance/parser/ecmascriptnext/numericSeparators/parser.numericSeparators.decmialNegative.ts
+++ b/tests/cases/conformance/parser/ecmascriptnext/numericSeparators/parser.numericSeparators.decmialNegative.ts
@@ -150,3 +150,9 @@ _0.0e-0
 
 // @filename: 51.ts
 0._
+
+// @filename: 52.ts
+09_0
+
+// @filename: 53.ts
+07_0