diff --git a/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCompiler.cs b/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCompiler.cs
index b26a627a8cf2e9..2733536bdbd57a 100644
--- a/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCompiler.cs
+++ b/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCompiler.cs
@@ -1337,7 +1337,7 @@ protected void GenerateFindFirstChar()
                 // ch = runtext[runtextpos];
                 // if (ch == lastChar) goto partialMatch;
                 Rightchar();
-                if (_boyerMoorePrefix.CaseInsensitive && ParticipatesInCaseConversion(chLast))
+                if (_boyerMoorePrefix.CaseInsensitive)
                 {
                     CallToLower();
                 }
diff --git a/src/libraries/System.Text.RegularExpressions/tests/Regex.Match.Tests.cs b/src/libraries/System.Text.RegularExpressions/tests/Regex.Match.Tests.cs
index 9ae78f8f91d2bb..aec0b8ccd8e22b 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/Regex.Match.Tests.cs
+++ b/src/libraries/System.Text.RegularExpressions/tests/Regex.Match.Tests.cs
@@ -15,6 +15,8 @@ public class RegexMatchTests
         public static IEnumerable<object[]> Match_Basic_TestData()
         {
             // pattern, input, options, beginning, length, expectedSuccess, expectedValue
+            yield return new object[] { @"H#", "#H#", RegexOptions.IgnoreCase, 0, 3, true, "H#" }; // https://github.com/dotnet/runtime/issues/39390
+            yield return new object[] { @"H#", "#H#", RegexOptions.None, 1, 2, true, "H#" };
 
             // Testing octal sequence matches: "\\060(\\061)?\\061"
             // Octal \061 is ASCII 49 ('1')