diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index a368a6a8f64aa..d4bee5742c9ff 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -8319,7 +8319,7 @@ namespace ts {
             return links.resolvedType;
         }
 
-        function addTypeToIntersection(typeSet: Type[], includes: TypeFlags, type: Type) {
+        function addTypeToIntersection(typeSet: Type[], includes: TypeFlags, type: Type, pos?: number) {
             const flags = type.flags;
             if (flags & TypeFlags.Intersection) {
                 return addTypesToIntersection(typeSet, includes, (<IntersectionType>type).types);
@@ -8336,7 +8336,12 @@ namespace ts {
                     !(flags & TypeFlags.Object && (<ObjectType>type).objectFlags & ObjectFlags.Anonymous &&
                     type.symbol && type.symbol.flags & (SymbolFlags.Function | SymbolFlags.Method) &&
                     containsIdenticalType(typeSet, type))) {
-                    typeSet.push(type);
+                    if (pos !== undefined) {
+                        typeSet.splice(pos, 0, type);
+                    }
+                    else {
+                        typeSet.push(type);
+                    }
                 }
             }
             return includes;
@@ -8382,6 +8387,10 @@ namespace ts {
             }
             const typeSet: Type[] = [];
             const includes = addTypesToIntersection(typeSet, 0, types);
+            return getIntersectionFromTypeSet(typeSet, includes, aliasSymbol, aliasTypeArguments);
+        }
+
+        function getIntersectionFromTypeSet(typeSet: Type[], includes: TypeFlags, aliasSymbol?: Symbol, aliasTypeArguments?: Type[]): Type {
             if (includes & TypeFlags.Never) {
                 return neverType;
             }
@@ -8420,6 +8429,74 @@ namespace ts {
             return type;
         }
 
+        /**
+         * This is a fast path replacement for `getIntersectionType` (though it should be interchangable) utilizing common properties of
+         * `keyof (A | B | C)` types to avoid deeply nesting type creation for all members of the inner union in the common
+         * case where the inner union members are mostly normal object types. In other scenarios, this is a bit more bookkeeping
+         * than is usually required.
+         *
+         * Essentially, all this does differently than `getIntersectionType` proper is locate the first union within the intersection,
+         * and the filter any other unions' members through the first union's members. This attempts to avoid recursively calling
+         * `getIntersectionType` as this process prevents any unions from being added to the intersection right at the start (provided
+         *  they are all literal-membered).
+         */
+        function getIntersectionTypeSpecializedForIndexType(types: Type[]) {
+            if (types.length === 0) {
+                return emptyObjectType;
+            }
+            if (types.length === 1) {
+                return types[0];
+            }
+            let maskedUnion: UnionType;
+            let masked: Type[];
+            const result: Type[] = [];
+            let includes: TypeFlags = 0;
+            let maskInjectionPosition = 0;
+            outerLoop: for (let i = 0; i < types.length; i++) {
+                const keySet = types[i];
+                if (keySet.flags & TypeFlags.Union) {
+                    if (!masked) {
+                        maskedUnion = keySet as UnionType;
+                        masked = (keySet as UnionType).types.slice();
+                        maskInjectionPosition = i;
+                    }
+                    else {
+                        const unfound = [];
+                        for (let i = 0; i < masked.length; i++) {
+                            const key = masked[i];
+                            if (key.flags & TypeFlags.Literal) {
+                                if (!some((keySet as UnionType).types, t => isTypeIdenticalTo(t, key))) {
+                                    unfound.push(i);
+                                }
+                            }
+                            else {
+                                // If a key type in the mask isn't a literal type (so is, eg, `number` or `symbol`)
+                                // We can't easily remove things by checking identity, so we fall back to just adding the
+                                // union normally
+                                includes = addTypeToIntersection(result, includes, getRegularTypeOfLiteralType(keySet));
+                                continue outerLoop;
+                            }
+                        }
+                        let priors = 0;
+                        for (const index of unfound) {
+                            orderedRemoveItemAt(masked, index - priors);
+                            priors++;
+                        }
+                    }
+                }
+                else {
+                    includes = addTypeToIntersection(result, includes, getRegularTypeOfLiteralType(keySet));
+                }
+            }
+            if (length(masked)) {
+                includes = addTypeToIntersection(result, includes, maskedUnion.types.length === masked.length ? maskedUnion : getUnionType(masked), maskInjectionPosition);
+            }
+            if (result.length === 0 && !includes) {
+                return neverType;
+            }
+            return getIntersectionFromTypeSet(result, includes);
+        }
+
         function getTypeFromIntersectionTypeNode(node: IntersectionTypeNode): Type {
             const links = getNodeLinks(node);
             if (!links.resolvedType) {
@@ -8468,7 +8545,7 @@ namespace ts {
         }
 
         function getIndexType(type: Type, stringsOnly = keyofStringsOnly): Type {
-            return type.flags & TypeFlags.Union ? getIntersectionType(map((<IntersectionType>type).types, t => getIndexType(t, stringsOnly))) :
+            return type.flags & TypeFlags.Union ? getIntersectionTypeSpecializedForIndexType(map((type as UnionType).types, t => getIndexType(t, stringsOnly))) :
                 type.flags & TypeFlags.Intersection ? getUnionType(map((<IntersectionType>type).types, t => getIndexType(t, stringsOnly))) :
                 maybeTypeOfKind(type, TypeFlags.InstantiableNonPrimitive) ? getIndexTypeForGenericType(<InstantiableType | UnionOrIntersectionType>type, stringsOnly) :
                 getObjectFlags(type) & ObjectFlags.Mapped ? getConstraintTypeFromMappedType(<MappedType>type) :
diff --git a/tests/baselines/reference/domKeyofUnionNoOOM.errors.txt b/tests/baselines/reference/domKeyofUnionNoOOM.errors.txt
new file mode 100644
index 0000000000000..367a67ee2ea1d
--- /dev/null
+++ b/tests/baselines/reference/domKeyofUnionNoOOM.errors.txt
@@ -0,0 +1,32 @@
+tests/cases/compiler/domKeyofUnionNoOOM.ts(19,12): error TS2536: Type 'T' cannot be used to index type 'HTMLElementTagNameMap'.
+tests/cases/compiler/domKeyofUnionNoOOM.ts(19,12): error TS2536: Type 'P' cannot be used to index type 'HTMLElementTagNameMap[T]'.
+
+
+==== tests/cases/compiler/domKeyofUnionNoOOM.ts (2 errors) ====
+    export function assertIsElement(node: Node | null): node is Element {
+    	let nodeType = node === null ? null : node.nodeType;
+    	return nodeType === 1;
+    }
+      
+    export function assertNodeTagName<
+    T extends keyof ElementTagNameMap,
+    U extends ElementTagNameMap[T]>(node: Node | null, tagName: T): node is U {
+    	if (assertIsElement(node)) {
+    		const nodeTagName = node.tagName.toLowerCase();
+    		return nodeTagName === tagName;
+    	}
+    	return false;
+    }
+      
+    export function assertNodeProperty<
+    	T extends keyof ElementTagNameMap,
+    	P extends keyof ElementTagNameMap[T],
+    	V extends HTMLElementTagNameMap[T][P]>(node: Node | null, tagName: T, prop: P, value: V) {
+    	          ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2536: Type 'T' cannot be used to index type 'HTMLElementTagNameMap'.
+    	          ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2536: Type 'P' cannot be used to index type 'HTMLElementTagNameMap[T]'.
+    	if (assertNodeTagName(node, tagName)) {
+    		node[prop];
+    	}
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/domKeyofUnionNoOOM.js b/tests/baselines/reference/domKeyofUnionNoOOM.js
new file mode 100644
index 0000000000000..73168e0265cb5
--- /dev/null
+++ b/tests/baselines/reference/domKeyofUnionNoOOM.js
@@ -0,0 +1,47 @@
+//// [domKeyofUnionNoOOM.ts]
+export function assertIsElement(node: Node | null): node is Element {
+	let nodeType = node === null ? null : node.nodeType;
+	return nodeType === 1;
+}
+  
+export function assertNodeTagName<
+T extends keyof ElementTagNameMap,
+U extends ElementTagNameMap[T]>(node: Node | null, tagName: T): node is U {
+	if (assertIsElement(node)) {
+		const nodeTagName = node.tagName.toLowerCase();
+		return nodeTagName === tagName;
+	}
+	return false;
+}
+  
+export function assertNodeProperty<
+	T extends keyof ElementTagNameMap,
+	P extends keyof ElementTagNameMap[T],
+	V extends HTMLElementTagNameMap[T][P]>(node: Node | null, tagName: T, prop: P, value: V) {
+	if (assertNodeTagName(node, tagName)) {
+		node[prop];
+	}
+}
+
+//// [domKeyofUnionNoOOM.js]
+"use strict";
+exports.__esModule = true;
+function assertIsElement(node) {
+    var nodeType = node === null ? null : node.nodeType;
+    return nodeType === 1;
+}
+exports.assertIsElement = assertIsElement;
+function assertNodeTagName(node, tagName) {
+    if (assertIsElement(node)) {
+        var nodeTagName = node.tagName.toLowerCase();
+        return nodeTagName === tagName;
+    }
+    return false;
+}
+exports.assertNodeTagName = assertNodeTagName;
+function assertNodeProperty(node, tagName, prop, value) {
+    if (assertNodeTagName(node, tagName)) {
+        node[prop];
+    }
+}
+exports.assertNodeProperty = assertNodeProperty;
diff --git a/tests/baselines/reference/domKeyofUnionNoOOM.symbols b/tests/baselines/reference/domKeyofUnionNoOOM.symbols
new file mode 100644
index 0000000000000..26a5b364e70d4
--- /dev/null
+++ b/tests/baselines/reference/domKeyofUnionNoOOM.symbols
@@ -0,0 +1,92 @@
+=== tests/cases/compiler/domKeyofUnionNoOOM.ts ===
+export function assertIsElement(node: Node | null): node is Element {
+>assertIsElement : Symbol(assertIsElement, Decl(domKeyofUnionNoOOM.ts, 0, 0))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 0, 32))
+>Node : Symbol(Node, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 0, 32))
+>Element : Symbol(Element, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+
+	let nodeType = node === null ? null : node.nodeType;
+>nodeType : Symbol(nodeType, Decl(domKeyofUnionNoOOM.ts, 1, 4))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 0, 32))
+>node.nodeType : Symbol(Node.nodeType, Decl(lib.dom.d.ts, --, --))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 0, 32))
+>nodeType : Symbol(Node.nodeType, Decl(lib.dom.d.ts, --, --))
+
+	return nodeType === 1;
+>nodeType : Symbol(nodeType, Decl(domKeyofUnionNoOOM.ts, 1, 4))
+}
+  
+export function assertNodeTagName<
+>assertNodeTagName : Symbol(assertNodeTagName, Decl(domKeyofUnionNoOOM.ts, 3, 1))
+
+T extends keyof ElementTagNameMap,
+>T : Symbol(T, Decl(domKeyofUnionNoOOM.ts, 5, 34))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.dom.d.ts, --, --))
+
+U extends ElementTagNameMap[T]>(node: Node | null, tagName: T): node is U {
+>U : Symbol(U, Decl(domKeyofUnionNoOOM.ts, 6, 34))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.dom.d.ts, --, --))
+>T : Symbol(T, Decl(domKeyofUnionNoOOM.ts, 5, 34))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 7, 32))
+>Node : Symbol(Node, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+>tagName : Symbol(tagName, Decl(domKeyofUnionNoOOM.ts, 7, 50))
+>T : Symbol(T, Decl(domKeyofUnionNoOOM.ts, 5, 34))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 7, 32))
+>U : Symbol(U, Decl(domKeyofUnionNoOOM.ts, 6, 34))
+
+	if (assertIsElement(node)) {
+>assertIsElement : Symbol(assertIsElement, Decl(domKeyofUnionNoOOM.ts, 0, 0))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 7, 32))
+
+		const nodeTagName = node.tagName.toLowerCase();
+>nodeTagName : Symbol(nodeTagName, Decl(domKeyofUnionNoOOM.ts, 9, 7))
+>node.tagName.toLowerCase : Symbol(String.toLowerCase, Decl(lib.es5.d.ts, --, --))
+>node.tagName : Symbol(Element.tagName, Decl(lib.dom.d.ts, --, --))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 7, 32))
+>tagName : Symbol(Element.tagName, Decl(lib.dom.d.ts, --, --))
+>toLowerCase : Symbol(String.toLowerCase, Decl(lib.es5.d.ts, --, --))
+
+		return nodeTagName === tagName;
+>nodeTagName : Symbol(nodeTagName, Decl(domKeyofUnionNoOOM.ts, 9, 7))
+>tagName : Symbol(tagName, Decl(domKeyofUnionNoOOM.ts, 7, 50))
+	}
+	return false;
+}
+  
+export function assertNodeProperty<
+>assertNodeProperty : Symbol(assertNodeProperty, Decl(domKeyofUnionNoOOM.ts, 13, 1))
+
+	T extends keyof ElementTagNameMap,
+>T : Symbol(T, Decl(domKeyofUnionNoOOM.ts, 15, 35))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.dom.d.ts, --, --))
+
+	P extends keyof ElementTagNameMap[T],
+>P : Symbol(P, Decl(domKeyofUnionNoOOM.ts, 16, 35))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.dom.d.ts, --, --))
+>T : Symbol(T, Decl(domKeyofUnionNoOOM.ts, 15, 35))
+
+	V extends HTMLElementTagNameMap[T][P]>(node: Node | null, tagName: T, prop: P, value: V) {
+>V : Symbol(V, Decl(domKeyofUnionNoOOM.ts, 17, 38))
+>HTMLElementTagNameMap : Symbol(HTMLElementTagNameMap, Decl(lib.dom.d.ts, --, --))
+>T : Symbol(T, Decl(domKeyofUnionNoOOM.ts, 15, 35))
+>P : Symbol(P, Decl(domKeyofUnionNoOOM.ts, 16, 35))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 18, 40))
+>Node : Symbol(Node, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+>tagName : Symbol(tagName, Decl(domKeyofUnionNoOOM.ts, 18, 58))
+>T : Symbol(T, Decl(domKeyofUnionNoOOM.ts, 15, 35))
+>prop : Symbol(prop, Decl(domKeyofUnionNoOOM.ts, 18, 70))
+>P : Symbol(P, Decl(domKeyofUnionNoOOM.ts, 16, 35))
+>value : Symbol(value, Decl(domKeyofUnionNoOOM.ts, 18, 79))
+>V : Symbol(V, Decl(domKeyofUnionNoOOM.ts, 17, 38))
+
+	if (assertNodeTagName(node, tagName)) {
+>assertNodeTagName : Symbol(assertNodeTagName, Decl(domKeyofUnionNoOOM.ts, 3, 1))
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 18, 40))
+>tagName : Symbol(tagName, Decl(domKeyofUnionNoOOM.ts, 18, 58))
+
+		node[prop];
+>node : Symbol(node, Decl(domKeyofUnionNoOOM.ts, 18, 40))
+>prop : Symbol(prop, Decl(domKeyofUnionNoOOM.ts, 18, 70))
+	}
+}
diff --git a/tests/baselines/reference/domKeyofUnionNoOOM.types b/tests/baselines/reference/domKeyofUnionNoOOM.types
new file mode 100644
index 0000000000000..e0e93b5b74d0d
--- /dev/null
+++ b/tests/baselines/reference/domKeyofUnionNoOOM.types
@@ -0,0 +1,107 @@
+=== tests/cases/compiler/domKeyofUnionNoOOM.ts ===
+export function assertIsElement(node: Node | null): node is Element {
+>assertIsElement : (node: Node) => node is Element
+>node : Node
+>Node : Node
+>null : null
+>node : any
+>Element : Element
+
+	let nodeType = node === null ? null : node.nodeType;
+>nodeType : number
+>node === null ? null : node.nodeType : number
+>node === null : boolean
+>node : Node
+>null : null
+>null : null
+>node.nodeType : number
+>node : Node
+>nodeType : number
+
+	return nodeType === 1;
+>nodeType === 1 : boolean
+>nodeType : number
+>1 : 1
+}
+  
+export function assertNodeTagName<
+>assertNodeTagName : <T extends "symbol" | "object" | "a" | "abbr" | "acronym" | "address" | "applet" | "area" | "article" | "aside" | "audio" | "b" | "base" | "basefont" | "bdo" | "big" | "blockquote" | "body" | "br" | "button" | "canvas" | "caption" | "center" | "cite" | "code" | "col" | "colgroup" | "data" | "datalist" | "dd" | "del" | "dfn" | "dir" | "div" | "dl" | "dt" | "em" | "embed" | "fieldset" | "figcaption" | "figure" | "font" | "footer" | "form" | "frame" | "frameset" | "h1" | "h2" | "h3" | "h4" | "h5" | "h6" | "head" | "header" | "hgroup" | "hr" | "html" | "i" | "iframe" | "img" | "input" | "ins" | "isindex" | "kbd" | "keygen" | "label" | "legend" | "li" | "link" | "listing" | "map" | "mark" | "marquee" | "menu" | "meta" | "meter" | "nav" | "nextid" | "nobr" | "noframes" | "noscript" | "ol" | "optgroup" | "option" | "output" | "p" | "param" | "picture" | "plaintext" | "pre" | "progress" | "q" | "rt" | "ruby" | "s" | "samp" | "script" | "section" | "select" | "slot" | "small" | "source" | "span" | "strike" | "strong" | "style" | "sub" | "sup" | "table" | "tbody" | "td" | "template" | "textarea" | "tfoot" | "th" | "thead" | "time" | "title" | "tr" | "track" | "tt" | "u" | "ul" | "var" | "video" | "wbr" | "xmp" | "circle" | "clippath" | "defs" | "desc" | "ellipse" | "feblend" | "fecolormatrix" | "fecomponenttransfer" | "fecomposite" | "feconvolvematrix" | "fediffuselighting" | "fedisplacementmap" | "fedistantlight" | "feflood" | "fefunca" | "fefuncb" | "fefuncg" | "fefuncr" | "fegaussianblur" | "feimage" | "femerge" | "femergenode" | "femorphology" | "feoffset" | "fepointlight" | "fespecularlighting" | "fespotlight" | "fetile" | "feturbulence" | "filter" | "foreignobject" | "g" | "image" | "line" | "lineargradient" | "marker" | "mask" | "metadata" | "path" | "pattern" | "polygon" | "polyline" | "radialgradient" | "rect" | "stop" | "svg" | "switch" | "text" | "textpath" | "tspan" | "use" | "view", U extends ElementTagNameMap[T]>(node: Node, tagName: T) => node is U
+
+T extends keyof ElementTagNameMap,
+>T : T
+>ElementTagNameMap : ElementTagNameMap
+
+U extends ElementTagNameMap[T]>(node: Node | null, tagName: T): node is U {
+>U : U
+>ElementTagNameMap : ElementTagNameMap
+>T : T
+>node : Node
+>Node : Node
+>null : null
+>tagName : T
+>T : T
+>node : any
+>U : U
+
+	if (assertIsElement(node)) {
+>assertIsElement(node) : boolean
+>assertIsElement : (node: Node) => node is Element
+>node : Node
+
+		const nodeTagName = node.tagName.toLowerCase();
+>nodeTagName : string
+>node.tagName.toLowerCase() : string
+>node.tagName.toLowerCase : () => string
+>node.tagName : string
+>node : Element
+>tagName : string
+>toLowerCase : () => string
+
+		return nodeTagName === tagName;
+>nodeTagName === tagName : boolean
+>nodeTagName : string
+>tagName : T
+	}
+	return false;
+>false : false
+}
+  
+export function assertNodeProperty<
+>assertNodeProperty : <T extends "symbol" | "object" | "a" | "abbr" | "acronym" | "address" | "applet" | "area" | "article" | "aside" | "audio" | "b" | "base" | "basefont" | "bdo" | "big" | "blockquote" | "body" | "br" | "button" | "canvas" | "caption" | "center" | "cite" | "code" | "col" | "colgroup" | "data" | "datalist" | "dd" | "del" | "dfn" | "dir" | "div" | "dl" | "dt" | "em" | "embed" | "fieldset" | "figcaption" | "figure" | "font" | "footer" | "form" | "frame" | "frameset" | "h1" | "h2" | "h3" | "h4" | "h5" | "h6" | "head" | "header" | "hgroup" | "hr" | "html" | "i" | "iframe" | "img" | "input" | "ins" | "isindex" | "kbd" | "keygen" | "label" | "legend" | "li" | "link" | "listing" | "map" | "mark" | "marquee" | "menu" | "meta" | "meter" | "nav" | "nextid" | "nobr" | "noframes" | "noscript" | "ol" | "optgroup" | "option" | "output" | "p" | "param" | "picture" | "plaintext" | "pre" | "progress" | "q" | "rt" | "ruby" | "s" | "samp" | "script" | "section" | "select" | "slot" | "small" | "source" | "span" | "strike" | "strong" | "style" | "sub" | "sup" | "table" | "tbody" | "td" | "template" | "textarea" | "tfoot" | "th" | "thead" | "time" | "title" | "tr" | "track" | "tt" | "u" | "ul" | "var" | "video" | "wbr" | "xmp" | "circle" | "clippath" | "defs" | "desc" | "ellipse" | "feblend" | "fecolormatrix" | "fecomponenttransfer" | "fecomposite" | "feconvolvematrix" | "fediffuselighting" | "fedisplacementmap" | "fedistantlight" | "feflood" | "fefunca" | "fefuncb" | "fefuncg" | "fefuncr" | "fegaussianblur" | "feimage" | "femerge" | "femergenode" | "femorphology" | "feoffset" | "fepointlight" | "fespecularlighting" | "fespotlight" | "fetile" | "feturbulence" | "filter" | "foreignobject" | "g" | "image" | "line" | "lineargradient" | "marker" | "mask" | "metadata" | "path" | "pattern" | "polygon" | "polyline" | "radialgradient" | "rect" | "stop" | "svg" | "switch" | "text" | "textpath" | "tspan" | "use" | "view", P extends keyof ElementTagNameMap[T], V extends HTMLElementTagNameMap[T][P]>(node: Node, tagName: T, prop: P, value: V) => void
+
+	T extends keyof ElementTagNameMap,
+>T : T
+>ElementTagNameMap : ElementTagNameMap
+
+	P extends keyof ElementTagNameMap[T],
+>P : P
+>ElementTagNameMap : ElementTagNameMap
+>T : T
+
+	V extends HTMLElementTagNameMap[T][P]>(node: Node | null, tagName: T, prop: P, value: V) {
+>V : V
+>HTMLElementTagNameMap : HTMLElementTagNameMap
+>T : T
+>P : P
+>node : Node
+>Node : Node
+>null : null
+>tagName : T
+>T : T
+>prop : P
+>P : P
+>value : V
+>V : V
+
+	if (assertNodeTagName(node, tagName)) {
+>assertNodeTagName(node, tagName) : boolean
+>assertNodeTagName : <T extends "symbol" | "object" | "a" | "abbr" | "acronym" | "address" | "applet" | "area" | "article" | "aside" | "audio" | "b" | "base" | "basefont" | "bdo" | "big" | "blockquote" | "body" | "br" | "button" | "canvas" | "caption" | "center" | "cite" | "code" | "col" | "colgroup" | "data" | "datalist" | "dd" | "del" | "dfn" | "dir" | "div" | "dl" | "dt" | "em" | "embed" | "fieldset" | "figcaption" | "figure" | "font" | "footer" | "form" | "frame" | "frameset" | "h1" | "h2" | "h3" | "h4" | "h5" | "h6" | "head" | "header" | "hgroup" | "hr" | "html" | "i" | "iframe" | "img" | "input" | "ins" | "isindex" | "kbd" | "keygen" | "label" | "legend" | "li" | "link" | "listing" | "map" | "mark" | "marquee" | "menu" | "meta" | "meter" | "nav" | "nextid" | "nobr" | "noframes" | "noscript" | "ol" | "optgroup" | "option" | "output" | "p" | "param" | "picture" | "plaintext" | "pre" | "progress" | "q" | "rt" | "ruby" | "s" | "samp" | "script" | "section" | "select" | "slot" | "small" | "source" | "span" | "strike" | "strong" | "style" | "sub" | "sup" | "table" | "tbody" | "td" | "template" | "textarea" | "tfoot" | "th" | "thead" | "time" | "title" | "tr" | "track" | "tt" | "u" | "ul" | "var" | "video" | "wbr" | "xmp" | "circle" | "clippath" | "defs" | "desc" | "ellipse" | "feblend" | "fecolormatrix" | "fecomponenttransfer" | "fecomposite" | "feconvolvematrix" | "fediffuselighting" | "fedisplacementmap" | "fedistantlight" | "feflood" | "fefunca" | "fefuncb" | "fefuncg" | "fefuncr" | "fegaussianblur" | "feimage" | "femerge" | "femergenode" | "femorphology" | "feoffset" | "fepointlight" | "fespecularlighting" | "fespotlight" | "fetile" | "feturbulence" | "filter" | "foreignobject" | "g" | "image" | "line" | "lineargradient" | "marker" | "mask" | "metadata" | "path" | "pattern" | "polygon" | "polyline" | "radialgradient" | "rect" | "stop" | "svg" | "switch" | "text" | "textpath" | "tspan" | "use" | "view", U extends ElementTagNameMap[T]>(node: Node, tagName: T) => node is U
+>node : Node
+>tagName : T
+
+		node[prop];
+>node[prop] : ElementTagNameMap[T][P]
+>node : ElementTagNameMap[T]
+>prop : P
+	}
+}
diff --git a/tests/cases/compiler/domKeyofUnionNoOOM.ts b/tests/cases/compiler/domKeyofUnionNoOOM.ts
new file mode 100644
index 0000000000000..f22aa24e071f7
--- /dev/null
+++ b/tests/cases/compiler/domKeyofUnionNoOOM.ts
@@ -0,0 +1,24 @@
+// @lib: dom,es6
+export function assertIsElement(node: Node | null): node is Element {
+	let nodeType = node === null ? null : node.nodeType;
+	return nodeType === 1;
+}
+  
+export function assertNodeTagName<
+T extends keyof ElementTagNameMap,
+U extends ElementTagNameMap[T]>(node: Node | null, tagName: T): node is U {
+	if (assertIsElement(node)) {
+		const nodeTagName = node.tagName.toLowerCase();
+		return nodeTagName === tagName;
+	}
+	return false;
+}
+  
+export function assertNodeProperty<
+	T extends keyof ElementTagNameMap,
+	P extends keyof ElementTagNameMap[T],
+	V extends HTMLElementTagNameMap[T][P]>(node: Node | null, tagName: T, prop: P, value: V) {
+	if (assertNodeTagName(node, tagName)) {
+		node[prop];
+	}
+}
\ No newline at end of file