diff --git a/CHANGELOG.md b/CHANGELOG.md
index bde6f995fa..95e4c7f81c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Drop support for Visual Studio 2022 VSIX ([PR](https://github.com/dotnet/roslynator/pull/1787))
   - Pin last 4.x release ([Roslynator 2022](https://marketplace.visualstudio.com/items?itemName=josefpihrt.Roslynator2022)) or use NuGet packages on Visual Studio 2022
 
+### Fixed
+
+- Fix analyzers [RCS1263](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1263) and [RCS1139](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1139) for C# 14 extension block documentation ([PR](https://github.com/dotnet/roslynator/pull/1799))
+
 ## [4.16.1] - 2026-08-16
 
 ### Fixed
diff --git a/src/Analyzers/CSharp/Analysis/SingleLineDocumentationCommentTriviaAnalyzer.cs b/src/Analyzers/CSharp/Analysis/SingleLineDocumentationCommentTriviaAnalyzer.cs
index f2272c54f5..c8aff5f8b3 100644
--- a/src/Analyzers/CSharp/Analysis/SingleLineDocumentationCommentTriviaAnalyzer.cs
+++ b/src/Analyzers/CSharp/Analysis/SingleLineDocumentationCommentTriviaAnalyzer.cs
@@ -185,14 +185,18 @@ private static void AnalyzeSingleLineDocumentationCommentTrivia(SyntaxNodeAnalys
             return;
         }
 
+        SyntaxNode parent = documentationComment.ParentTrivia.Token.Parent;
+
         if (!containsSummaryElement
-            && !containsContentElement)
+            && !containsContentElement
+#if ROSLYN_5_0
+            && parent?.IsKind(SyntaxKind.ExtensionBlockDeclaration) != true
+#endif
+            )
         {
             ReportDiagnosticIfEffective(context, DiagnosticRules.AddSummaryElementToDocumentationComment, documentationComment);
         }
 
-        SyntaxNode parent = documentationComment.ParentTrivia.Token.Parent;
-
         bool invalidReference = DiagnosticRules.InvalidReferenceInDocumentationComment.IsEffective(context);
         bool orderParams = DiagnosticRules.OrderElementsInDocumentationComment.IsEffective(context);
         bool addParam = DiagnosticRules.AddParamElementToDocumentationComment.IsEffective(context);
diff --git a/src/CSharp/CSharp/CSharpUtility.cs b/src/CSharp/CSharp/CSharpUtility.cs
index d6627c6381..64e3b265a2 100644
--- a/src/CSharp/CSharp/CSharpUtility.cs
+++ b/src/CSharp/CSharp/CSharpUtility.cs
@@ -688,6 +688,10 @@ public static SeparatedSyntaxList<ParameterSyntax> GetParameters(SyntaxNode decl
             case SyntaxKind.StructDeclaration:
             case SyntaxKind.InterfaceDeclaration:
                 return ((TypeDeclarationSyntax)declaration).ParameterList;
+#endif
+#if ROSLYN_5_0
+            case SyntaxKind.ExtensionBlockDeclaration:
+                return ((ExtensionBlockDeclarationSyntax)declaration).ParameterList;
 #endif
             default:
                 return null;
@@ -720,6 +724,10 @@ public static SeparatedSyntaxList<TypeParameterSyntax> GetTypeParameters(SyntaxN
             case SyntaxKind.RecordStructDeclaration:
 #endif
                 return ((RecordDeclarationSyntax)declaration).TypeParameterList;
+#if ROSLYN_5_0
+            case SyntaxKind.ExtensionBlockDeclaration:
+                return ((ExtensionBlockDeclarationSyntax)declaration).TypeParameterList;
+#endif
             default:
                 return null;
         }
diff --git a/src/Tests/Analyzers.Tests/RCS1139AddSummaryElementToDocumentationCommentTests.cs b/src/Tests/Analyzers.Tests/RCS1139AddSummaryElementToDocumentationCommentTests.cs
index 4440d63aa0..c24c76bee2 100644
--- a/src/Tests/Analyzers.Tests/RCS1139AddSummaryElementToDocumentationCommentTests.cs
+++ b/src/Tests/Analyzers.Tests/RCS1139AddSummaryElementToDocumentationCommentTests.cs
@@ -50,4 +50,20 @@ partial class C
 }
 ");
     }
+
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.AddSummaryElementToDocumentationComment)]
+    public async Task TestNoDiagnostic_ExtensionBlock_WithoutSummary()
+    {
+        await VerifyNoDiagnosticAsync("""
+static class C
+{
+    /// <param name="x">x</param>
+    /// <typeparam name="T">T</typeparam>
+    extension<T>(T x) where T : struct
+    {
+        public int M() => 0;
+    }
+}
+""");
+    }
 }
diff --git a/src/Tests/Analyzers.Tests/RCS1263InvalidReferenceInDocumentationCommentTests.cs b/src/Tests/Analyzers.Tests/RCS1263InvalidReferenceInDocumentationCommentTests.cs
index 8d980db15c..08046384f2 100644
--- a/src/Tests/Analyzers.Tests/RCS1263InvalidReferenceInDocumentationCommentTests.cs
+++ b/src/Tests/Analyzers.Tests/RCS1263InvalidReferenceInDocumentationCommentTests.cs
@@ -205,6 +205,47 @@ public struct Foo(string value)
 {
     public string Value { get; } = value;
 }
+""");
+    }
+
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.InvalidReferenceInDocumentationComment)]
+    public async Task TestNoDiagnostic_ExtensionBlock_ParamAndTypeParam()
+    {
+        await VerifyNoDiagnosticAsync("""
+static class C
+{
+    /// <param name="x">x</param>
+    /// <typeparam name="T">T</typeparam>
+    extension<T>(T x) where T : struct
+    {
+        public int M() => 0;
+    }
+}
+""");
+    }
+
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.InvalidReferenceInDocumentationComment)]
+    public async Task Test_ExtensionBlock_InvalidParamName()
+    {
+        await VerifyDiagnosticAndFixAsync("""
+static class C
+{
+    /// <param name="[|missing|]"></param>
+    /// <typeparam name="T">T</typeparam>
+    extension<T>(T x) where T : struct
+    {
+        public int M() => 0;
+    }
+}
+""", """
+static class C
+{
+    /// <typeparam name="T">T</typeparam>
+    extension<T>(T x) where T : struct
+    {
+        public int M() => 0;
+    }
+}
 """);
     }
 }