diff --git a/StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/DocumentationRules/SA1649CSharp10UnitTests.cs b/StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/DocumentationRules/SA1649CSharp10UnitTests.cs
index 3ae105437..e63b2cd68 100644
--- a/StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/DocumentationRules/SA1649CSharp10UnitTests.cs
+++ b/StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/DocumentationRules/SA1649CSharp10UnitTests.cs
@@ -3,9 +3,47 @@
 
 namespace StyleCop.Analyzers.Test.CSharp10.DocumentationRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
     using StyleCop.Analyzers.Test.CSharp9.DocumentationRules;
+    using StyleCop.Analyzers.Test.Helpers;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.CustomDiagnosticVerifier<
+        StyleCop.Analyzers.DocumentationRules.SA1649FileNameMustMatchTypeName>;
 
     public class SA1649CSharp10UnitTests : SA1649CSharp9UnitTests
     {
+        /// <summary>
+        /// Verifies that the file name is based on the first type.
+        /// </summary>
+        /// <param name="typeKeyword">The type keyword to use during the test.</param>
+        /// <returns>A <see cref="Task"/> representing the asynchronous unit test.</returns>
+        [Theory]
+        [MemberData(nameof(CommonMemberData.TypeDeclarationKeywords), MemberType = typeof(CommonMemberData))]
+        [WorkItem(3435, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3435")]
+        public async Task VerifyFirstTypeIsUsedWithFileScopedNamespacesAsync(string typeKeyword)
+        {
+            var testCode = $@"namespace TestNamespace;
+
+public enum IgnoredEnum {{ }}
+public delegate void IgnoredDelegate();
+
+{GetTypeDeclaration(typeKeyword, "TestType", diagnosticKey: 0)}
+
+{GetTypeDeclaration(typeKeyword, "TestType2")}
+";
+            var fixedCode = $@"namespace TestNamespace;
+
+public enum IgnoredEnum {{ }}
+public delegate void IgnoredDelegate();
+
+{GetTypeDeclaration(typeKeyword, "TestType")}
+
+{GetTypeDeclaration(typeKeyword, "TestType2")}
+";
+
+            var expectedDiagnostic = Diagnostic().WithLocation(0);
+            await VerifyCSharpFixAsync("TestType2.cs", testCode, StyleCopSettings, expectedDiagnostic, "TestType.cs", fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }
diff --git a/StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/MaintainabilityRules/SA1402CSharp10ForClassUnitTests.cs b/StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/MaintainabilityRules/SA1402CSharp10ForClassUnitTests.cs
index cfade8dbc..41e3c74a8 100644
--- a/StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/MaintainabilityRules/SA1402CSharp10ForClassUnitTests.cs
+++ b/StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/MaintainabilityRules/SA1402CSharp10ForClassUnitTests.cs
@@ -3,9 +3,41 @@
 
 namespace StyleCop.Analyzers.Test.CSharp10.MaintainabilityRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
     using StyleCop.Analyzers.Test.CSharp9.MaintainabilityRules;
+    using Xunit;
 
     public class SA1402CSharp10ForClassUnitTests : SA1402CSharp9ForClassUnitTests
     {
+        [Fact]
+        [WorkItem(3435, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3435")]
+        public async Task VerifyTwoClassesWithFileScopedNamespacesAsync()
+        {
+            var testCode = $@"namespace TestNamespace;
+
+public class TestClass1 {{ }}
+public class {{|#0:TestClass2|}} {{ }}
+";
+            var fixedCode1 = $@"namespace TestNamespace;
+
+public class TestClass1 {{ }}
+";
+            var fixedCode2 = $@"namespace TestNamespace;
+public class TestClass2 {{ }}
+";
+
+            var expectedDiagnostic = this.Diagnostic().WithLocation(0);
+            await this.VerifyCSharpFixAsync(
+                testCode,
+                this.GetSettings(),
+                expectedDiagnostic,
+                new[]
+                {
+                    ("/0/Test0.cs", fixedCode1),
+                    ("TestClass2.cs", fixedCode2),
+                },
+                CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }
diff --git a/StyleCop.Analyzers/StyleCop.Analyzers.Test/DocumentationRules/SA1649UnitTests.cs b/StyleCop.Analyzers/StyleCop.Analyzers.Test/DocumentationRules/SA1649UnitTests.cs
index ccb105e31..5f2bf72bb 100644
--- a/StyleCop.Analyzers/StyleCop.Analyzers.Test/DocumentationRules/SA1649UnitTests.cs
+++ b/StyleCop.Analyzers/StyleCop.Analyzers.Test/DocumentationRules/SA1649UnitTests.cs
@@ -17,7 +17,7 @@ namespace StyleCop.Analyzers.Test.DocumentationRules
     /// </summary>
     public class SA1649UnitTests
     {
-        private const string MetadataSettings = @"
+        protected const string MetadataSettings = @"
 {
   ""settings"": {
     ""documentationRules"": {
@@ -27,7 +27,7 @@ public class SA1649UnitTests
 }
 ";
 
-        private const string StyleCopSettings = @"
+        protected const string StyleCopSettings = @"
 {
   ""settings"": {
     ""documentationRules"": {
@@ -331,7 +331,7 @@ public class Class2
             await VerifyCSharpDiagnosticAsync("Class1.cs", testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
         }
 
-        private static string GetTypeDeclaration(string typeKind, string typeName, int? diagnosticKey = null)
+        protected static string GetTypeDeclaration(string typeKind, string typeName, int? diagnosticKey = null)
         {
             if (diagnosticKey is not null)
             {
@@ -345,7 +345,7 @@ private static string GetTypeDeclaration(string typeKind, string typeName, int?
             };
         }
 
-        private static Task VerifyCSharpDiagnosticAsync(string fileName, string source, DiagnosticResult[] expected, CancellationToken cancellationToken)
+        protected static Task VerifyCSharpDiagnosticAsync(string fileName, string source, DiagnosticResult[] expected, CancellationToken cancellationToken)
         {
             var test = new StyleCopCodeFixVerifier<SA1649FileNameMustMatchTypeName, SA1649CodeFixProvider>.CSharpTest()
             {
@@ -356,10 +356,10 @@ private static Task VerifyCSharpDiagnosticAsync(string fileName, string source,
             return test.RunAsync(cancellationToken);
         }
 
-        private static Task VerifyCSharpFixAsync(string oldFileName, string source, string testSettings, DiagnosticResult expected, string newFileName, string fixedSource, CancellationToken cancellationToken)
+        protected static Task VerifyCSharpFixAsync(string oldFileName, string source, string testSettings, DiagnosticResult expected, string newFileName, string fixedSource, CancellationToken cancellationToken)
             => VerifyCSharpFixAsync(oldFileName, source, testSettings, new[] { expected }, newFileName, fixedSource, cancellationToken);
 
-        private static Task VerifyCSharpFixAsync(string oldFileName, string source, string testSettings, DiagnosticResult[] expected, string newFileName, string fixedSource, CancellationToken cancellationToken)
+        protected static Task VerifyCSharpFixAsync(string oldFileName, string source, string testSettings, DiagnosticResult[] expected, string newFileName, string fixedSource, CancellationToken cancellationToken)
         {
             var test = new StyleCopCodeFixVerifier<SA1649FileNameMustMatchTypeName, SA1649CodeFixProvider>.CSharpTest()
             {
diff --git a/StyleCop.Analyzers/StyleCop.Analyzers/DocumentationRules/SA1649FileNameMustMatchTypeName.cs b/StyleCop.Analyzers/StyleCop.Analyzers/DocumentationRules/SA1649FileNameMustMatchTypeName.cs
index 125fc6e4d..b087bb726 100644
--- a/StyleCop.Analyzers/StyleCop.Analyzers/DocumentationRules/SA1649FileNameMustMatchTypeName.cs
+++ b/StyleCop.Analyzers/StyleCop.Analyzers/DocumentationRules/SA1649FileNameMustMatchTypeName.cs
@@ -11,6 +11,7 @@ namespace StyleCop.Analyzers.DocumentationRules
     using Microsoft.CodeAnalysis.CSharp.Syntax;
     using Microsoft.CodeAnalysis.Diagnostics;
     using StyleCop.Analyzers.Helpers;
+    using StyleCop.Analyzers.Lightup;
     using StyleCop.Analyzers.Settings.ObjectModel;
 
     /// <summary>
@@ -97,13 +98,13 @@ public static void HandleSyntaxTree(SyntaxTreeAnalysisContext context, StyleCopS
             private static MemberDeclarationSyntax GetFirstTypeDeclaration(SyntaxNode root)
             {
                 // Prefer to find the first type which is a true TypeDeclarationSyntax
-                MemberDeclarationSyntax firstTypeDeclaration = root.DescendantNodes(descendIntoChildren: node => node.IsKind(SyntaxKind.CompilationUnit) || node.IsKind(SyntaxKind.NamespaceDeclaration))
+                MemberDeclarationSyntax firstTypeDeclaration = root.DescendantNodes(descendIntoChildren: node => node.IsKind(SyntaxKind.CompilationUnit) || node.IsKind(SyntaxKind.NamespaceDeclaration) || node.IsKind(SyntaxKindEx.FileScopedNamespaceDeclaration))
                     .OfType<TypeDeclarationSyntax>()
                     .FirstOrDefault();
 
                 // If no TypeDeclarationSyntax is found, expand the search to any type declaration as long as only one
                 // is present
-                var expandedTypeDeclarations = root.DescendantNodes(descendIntoChildren: node => node.IsKind(SyntaxKind.CompilationUnit) || node.IsKind(SyntaxKind.NamespaceDeclaration))
+                var expandedTypeDeclarations = root.DescendantNodes(descendIntoChildren: node => node.IsKind(SyntaxKind.CompilationUnit) || node.IsKind(SyntaxKind.NamespaceDeclaration) || node.IsKind(SyntaxKindEx.FileScopedNamespaceDeclaration))
                     .OfType<MemberDeclarationSyntax>()
                     .Where(node => node is BaseTypeDeclarationSyntax || node.IsKind(SyntaxKind.DelegateDeclaration))
                     .ToList();
diff --git a/StyleCop.Analyzers/StyleCop.Analyzers/MaintainabilityRules/SA1402FileMayOnlyContainASingleType.cs b/StyleCop.Analyzers/StyleCop.Analyzers/MaintainabilityRules/SA1402FileMayOnlyContainASingleType.cs
index 35e153783..18194e065 100644
--- a/StyleCop.Analyzers/StyleCop.Analyzers/MaintainabilityRules/SA1402FileMayOnlyContainASingleType.cs
+++ b/StyleCop.Analyzers/StyleCop.Analyzers/MaintainabilityRules/SA1402FileMayOnlyContainASingleType.cs
@@ -12,6 +12,7 @@ namespace StyleCop.Analyzers.MaintainabilityRules
     using Microsoft.CodeAnalysis.CSharp.Syntax;
     using Microsoft.CodeAnalysis.Diagnostics;
     using StyleCop.Analyzers.Helpers;
+    using StyleCop.Analyzers.Lightup;
     using StyleCop.Analyzers.Settings.ObjectModel;
 
     /// <summary>
@@ -99,7 +100,7 @@ private static IEnumerable<MemberDeclarationSyntax> GetTopLevelTypeDeclarations(
 
         private static bool ContainsTopLevelTypeDeclarations(SyntaxNode node)
         {
-            return node.IsKind(SyntaxKind.CompilationUnit) || node.IsKind(SyntaxKind.NamespaceDeclaration);
+            return node.IsKind(SyntaxKind.CompilationUnit) || node.IsKind(SyntaxKind.NamespaceDeclaration) || node.IsKind(SyntaxKindEx.FileScopedNamespaceDeclaration);
         }
 
         private static bool IsRelevantType(SyntaxNode node, StyleCopSettings settings)