diff --git a/sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.Close.cs b/sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.Close.cs
index 02852348..fe837916 100644
--- a/sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.Close.cs
+++ b/sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.Close.cs
@@ -290,6 +290,33 @@ public void Close()
             }
         }
 
+        // The method class output builders are emitted here, before the helper types, so that in
+        // single-file mode the helper types are appended at the bottom of the shared namespace
+        // rather than in the middle of the generated output. In multi-file mode the method classes
+        // were already written directly above, so both dictionaries are empty and these loops are a
+        // no-op.
+
+        if (leaveStreamOpen)
+        {
+            Debug.Assert(stream is not null);
+
+            foreach (var entry in methodClassOutputBuilders)
+            {
+                CloseOutputBuilder(stream, entry.Value, isMethodClass: true, leaveStreamOpen, emitNamespaceDeclaration);
+                emitNamespaceDeclaration = false;
+            }
+
+            foreach (var entry in methodClassTestOutputBuilders)
+            {
+                CloseOutputBuilder(testStream ?? stream, entry.Value, isMethodClass: true, leaveStreamOpen, emitNamespaceDeclaration);
+            }
+        }
+        else
+        {
+            Debug.Assert(methodClassOutputBuilders.Count == 0);
+            Debug.Assert(methodClassTestOutputBuilders.Count == 0);
+        }
+
         if (generateHelperTypes)
         {
             // In single-file mode the helper types are emitted inside the shared namespace and are
@@ -349,16 +376,6 @@ public void Close()
         {
             Debug.Assert(stream is not null);
 
-            foreach (var entry in methodClassOutputBuilders)
-            {
-                CloseOutputBuilder(stream, entry.Value, isMethodClass: true, leaveStreamOpen, emitNamespaceDeclaration);
-            }
-
-            foreach (var entry in methodClassTestOutputBuilders)
-            {
-                CloseOutputBuilder(testStream ?? stream, entry.Value, isMethodClass: true, leaveStreamOpen, emitNamespaceDeclaration);
-            }
-
             using var sw = new StreamWriter(stream, s_defaultStreamWriterEncoding, DefaultStreamWriterBufferSize, leaveStreamOpen);
             sw.NewLine = "\n";
 
diff --git a/tests/ClangSharp.PInvokeGenerator.UnitTests/HelperTypesTest.cs b/tests/ClangSharp.PInvokeGenerator.UnitTests/HelperTypesTest.cs
index 3d2d70e9..04a21397 100644
--- a/tests/ClangSharp.PInvokeGenerator.UnitTests/HelperTypesTest.cs
+++ b/tests/ClangSharp.PInvokeGenerator.UnitTests/HelperTypesTest.cs
@@ -6,11 +6,14 @@
 namespace ClangSharp.UnitTests;
 
 /// <summary>
-/// Regression test for https://github.com/dotnet/ClangSharp/issues/657.
+/// Regression tests for https://github.com/dotnet/ClangSharp/issues/657 and
+/// https://github.com/dotnet/ClangSharp/issues/429.
 /// When <c>generate-helper-types</c> is used with a single output file, the helper types must be
 /// emitted inside the shared namespace with their usings hoisted to the top of the file, rather than
 /// each helper emitting its own <c>using</c> directives and <c>namespace</c> wrapper (which produced
-/// invalid C# with nested namespaces, usings after a namespace, and a stray trailing brace).
+/// invalid C# with nested namespaces, usings after a namespace, and a stray trailing brace). The
+/// helper types must also be emitted at the bottom of the shared namespace, after the deferred method
+/// class, rather than in the middle of the generated output.
 /// </summary>
 [Platform("win")]
 public sealed class HelperTypesTest : PInvokeGeneratorTest
@@ -122,6 +125,153 @@ public NativeTypeNameAttribute(string name)
     public string Name => _name;
 }
 
+/// <summary>Defines the annotation found in a native declaration.</summary>
+[AttributeUsage(AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.ReturnValue, AllowMultiple = true, Inherited = false)]
+[Conditional(""DEBUG"")]
+internal sealed partial class NativeAnnotationAttribute : Attribute
+{
+    private readonly string _annotation;
+
+    /// <summary>Initializes a new instance of the <see cref=""NativeAnnotationAttribute"" /> class.</summary>
+    /// <param name=""annotation"">The annotation that was used in the native declaration.</param>
+    public NativeAnnotationAttribute(string annotation)
+    {
+        _annotation = annotation;
+    }
+
+    /// <summary>Gets the annotation that was used in the native declaration.</summary>
+    public string Annotation => _annotation;
+}
+";
+
+        return ValidateGeneratedCSharpLatestWindowsBindingsAsync(inputContents, expectedOutputContents, additionalConfigOptions: PInvokeGeneratorConfigurationOptions.GenerateHelperTypes | PInvokeGeneratorConfigurationOptions.GenerateFileScopedNamespaces);
+    }
+
+    [Test]
+    public Task HelperTypesEmittedAfterMethodClass()
+    {
+        var inputContents = @"struct SRC_DATA
+{
+    const float *data_in;
+    long input_frames;
+};
+
+extern ""C"" void MyFunction();
+";
+
+        var expectedOutputContents = @"using System;
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+
+namespace ClangSharp.Test
+{
+    public unsafe partial struct SRC_DATA
+    {
+        [NativeTypeName(""const float *"")]
+        public float* data_in;
+
+        [NativeTypeName(""long"")]
+        public int input_frames;
+    }
+
+    public static partial class Methods
+    {
+        [DllImport(""ClangSharpPInvokeGenerator"", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
+        public static extern void MyFunction();
+    }
+
+    /// <summary>Defines the type of a member as it was used in the native signature.</summary>
+    [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.ReturnValue, AllowMultiple = false, Inherited = true)]
+    [Conditional(""DEBUG"")]
+    internal sealed partial class NativeTypeNameAttribute : Attribute
+    {
+        private readonly string _name;
+
+        /// <summary>Initializes a new instance of the <see cref=""NativeTypeNameAttribute"" /> class.</summary>
+        /// <param name=""name"">The name of the type that was used in the native signature.</param>
+        public NativeTypeNameAttribute(string name)
+        {
+            _name = name;
+        }
+
+        /// <summary>Gets the name of the type that was used in the native signature.</summary>
+        public string Name => _name;
+    }
+
+    /// <summary>Defines the annotation found in a native declaration.</summary>
+    [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.ReturnValue, AllowMultiple = true, Inherited = false)]
+    [Conditional(""DEBUG"")]
+    internal sealed partial class NativeAnnotationAttribute : Attribute
+    {
+        private readonly string _annotation;
+
+        /// <summary>Initializes a new instance of the <see cref=""NativeAnnotationAttribute"" /> class.</summary>
+        /// <param name=""annotation"">The annotation that was used in the native declaration.</param>
+        public NativeAnnotationAttribute(string annotation)
+        {
+            _annotation = annotation;
+        }
+
+        /// <summary>Gets the annotation that was used in the native declaration.</summary>
+        public string Annotation => _annotation;
+    }
+}
+";
+
+        return ValidateGeneratedCSharpLatestWindowsBindingsAsync(inputContents, expectedOutputContents, additionalConfigOptions: PInvokeGeneratorConfigurationOptions.GenerateHelperTypes);
+    }
+
+    [Test]
+    public Task HelperTypesEmittedAfterMethodClassFileScoped()
+    {
+        var inputContents = @"struct SRC_DATA
+{
+    const float *data_in;
+    long input_frames;
+};
+
+extern ""C"" void MyFunction();
+";
+
+        var expectedOutputContents = @"using System;
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+
+namespace ClangSharp.Test;
+
+public unsafe partial struct SRC_DATA
+{
+    [NativeTypeName(""const float *"")]
+    public float* data_in;
+
+    [NativeTypeName(""long"")]
+    public int input_frames;
+}
+
+public static partial class Methods
+{
+    [DllImport(""ClangSharpPInvokeGenerator"", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
+    public static extern void MyFunction();
+}
+
+/// <summary>Defines the type of a member as it was used in the native signature.</summary>
+[AttributeUsage(AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.ReturnValue, AllowMultiple = false, Inherited = true)]
+[Conditional(""DEBUG"")]
+internal sealed partial class NativeTypeNameAttribute : Attribute
+{
+    private readonly string _name;
+
+    /// <summary>Initializes a new instance of the <see cref=""NativeTypeNameAttribute"" /> class.</summary>
+    /// <param name=""name"">The name of the type that was used in the native signature.</param>
+    public NativeTypeNameAttribute(string name)
+    {
+        _name = name;
+    }
+
+    /// <summary>Gets the name of the type that was used in the native signature.</summary>
+    public string Name => _name;
+}
+
 /// <summary>Defines the annotation found in a native declaration.</summary>
 [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.ReturnValue, AllowMultiple = true, Inherited = false)]
 [Conditional(""DEBUG"")]