diff --git a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
index a8548a3bd0bfce..4f21419199016b 100644
--- a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
+++ b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
@@ -104,8 +104,9 @@ operation is not (IInvocationOperation or IObjectCreationOperation))
             }
 
             // Get the parent type declaration so that we can inspect its methods as well as check if we need to add the partial keyword.
+            // Skip extension blocks, as they can't be partial and can't contain generated regex members.
             SyntaxNode? typeDeclarationOrCompilationUnit =
-                nodeToFix.Ancestors().OfType<TypeDeclarationSyntax>().FirstOrDefault() ??
+                nodeToFix.Ancestors().OfType<TypeDeclarationSyntax>().FirstOrDefault(t => t is not ExtensionBlockDeclarationSyntax) ??
                 await nodeToFix.SyntaxTree.GetRootAsync(cancellationToken).ConfigureAwait(false);
 
             // Calculate what name should be used for the generated static partial property.
@@ -210,7 +211,7 @@ where modifier.Kind() is SyntaxKind.PublicKeyword or SyntaxKind.PrivateKeyword o
                         SyntaxFactory.AccessorDeclaration(SyntaxKind.GetAccessorDeclaration)
                             .WithSemicolonToken(SyntaxFactory.Token(SyntaxKind.SemicolonToken)))));
 
-            var typeDeclarationOrCompilationUnit = nodeToFix.Ancestors().OfType<TypeDeclarationSyntax>().FirstOrDefault() ?? root;
+            var typeDeclarationOrCompilationUnit = nodeToFix.Ancestors().OfType<TypeDeclarationSyntax>().FirstOrDefault(t => t is not ExtensionBlockDeclarationSyntax) ?? root;
 
             ImmutableArray<IArgumentOperation> operationArguments =
                 operation is IObjectCreationOperation objectCreation ?
@@ -255,7 +256,7 @@ operation is not (IInvocationOperation or IObjectCreationOperation))
                         SyntaxFactory.AccessorDeclaration(SyntaxKind.GetAccessorDeclaration)
                             .WithSemicolonToken(SyntaxFactory.Token(SyntaxKind.SemicolonToken)))));
 
-            var typeDeclarationOrCompilationUnit = nodeToFix.Ancestors().OfType<TypeDeclarationSyntax>().FirstOrDefault() ?? root;
+            var typeDeclarationOrCompilationUnit = nodeToFix.Ancestors().OfType<TypeDeclarationSyntax>().FirstOrDefault(t => t is not ExtensionBlockDeclarationSyntax) ?? root;
 
             ImmutableArray<IArgumentOperation> operationArguments =
                 operation is IObjectCreationOperation objectCreation ?
@@ -342,7 +343,7 @@ private static Document TryAddNewMember(
             var trackedRoot = root.TrackNodes(parent is null ? [nodeToFix] : [nodeToFix, parent]);
 
             root = trackedRoot.ReplaceNodes(
-                trackedRoot.GetCurrentNode(nodeToFix)!.Ancestors().OfType<TypeDeclarationSyntax>(),
+                trackedRoot.GetCurrentNode(nodeToFix)!.Ancestors().OfType<TypeDeclarationSyntax>().Where(t => t is not ExtensionBlockDeclarationSyntax),
                 (_, typeDeclaration) =>
                     typeDeclaration.Modifiers.Any(m => m.IsKind(SyntaxKind.PartialKeyword)) ?
                         typeDeclaration :
diff --git a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
index 061c34787063ba..24b7308fe93fd4 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
+++ b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
@@ -969,6 +969,66 @@ public void Foo()
             await VerifyCS.VerifyCodeFixAsync(test, fixedSource);
         }
 
+        [Fact]
+        public async Task CodeFixSupportsExtensionMembers_StaticInvocation()
+        {
+            string test = @"using System.Text.RegularExpressions;
+
+static class Foo
+{
+    extension(string value)
+    {
+        public bool Test() => [|Regex.IsMatch|](value, @""\d+"");
+    }
+}
+";
+            string fixedSource = @"using System.Text.RegularExpressions;
+
+static partial class Foo
+{
+    extension(string value)
+    {
+        public bool Test() => MyRegex.IsMatch(value);
+    }
+
+    [GeneratedRegex(@""\d+"")]
+    private static partial Regex MyRegex { get; }
+}
+";
+
+            await VerifyCS.VerifyCodeFixAsync(test, fixedSource);
+        }
+
+        [Fact]
+        public async Task CodeFixSupportsExtensionMembers_Constructor()
+        {
+            string test = @"using System.Text.RegularExpressions;
+
+static class Foo
+{
+    extension(string value)
+    {
+        public Regex GetRegex() => [|new Regex|](@""\d+"");
+    }
+}
+";
+            string fixedSource = @"using System.Text.RegularExpressions;
+
+static partial class Foo
+{
+    extension(string value)
+    {
+        public Regex GetRegex() => MyRegex;
+    }
+
+    [GeneratedRegex(@""\d+"")]
+    private static partial Regex MyRegex { get; }
+}
+";
+
+            await VerifyCS.VerifyCodeFixAsync(test, fixedSource);
+        }
+
         [Theory]
         [MemberData(nameof(InvocationTypes))]
         public async Task NoDiagnosticForRegexOptionsNonBacktracking(InvocationType invocationType)