diff --git a/README.md b/README.md
index 47a4f28..99a14ef 100644
--- a/README.md
+++ b/README.md
@@ -42,7 +42,7 @@ public readonly partial struct Int32OrString
 #nullable enable
 namespace EfficientUnionGenerator.SampleApp.SimpleUnionOfInt32OrString;
 
-
+[System.Runtime.CompilerServices.Union]
 partial struct Int32OrString
 {
     private enum __TypeSpecifier : byte
@@ -146,7 +146,7 @@ public readonly partial struct SignedInteger
 #nullable enable
 namespace EfficientUnionGenerator.SampleApp.SimpleUnionOfSignedInteger;
 
-
+[System.Runtime.CompilerServices.Union]
 partial struct SignedInteger
 {
     private enum __TypeSpecifier : byte
@@ -312,7 +312,7 @@ public static class Program
 #nullable enable
 namespace EfficientUnionGenerator.SampleApp.PositiveOnlyIntOrFloat;
 
-
+[System.Runtime.CompilerServices.Union]
 partial struct PositiveOnlyIntOrFloat
 {
     private enum __TypeSpecifier : uint
@@ -444,7 +444,7 @@ public readonly partial struct ElfHeader
 #nullable enable
 namespace EfficientUnionGenerator.SampleApp.ElfHeader;
 
-
+[System.Runtime.CompilerServices.Union]
 partial struct ElfHeader
 {
     private enum __TypeSpecifier : ulong
diff --git a/src/EfficientUnionGenerator/Generator.cs b/src/EfficientUnionGenerator/Generator.cs
index 4983cba..1d40ba6 100644
--- a/src/EfficientUnionGenerator/Generator.cs
+++ b/src/EfficientUnionGenerator/Generator.cs
@@ -97,9 +97,11 @@ private static void EmitUnionType(SourceProductionContext context, UnionTypeDefi
         sb.AppendAutoGeneratedComment();
         sb.AppendLine("#nullable enable");
         sb.AppendNamespaceDeclaration();
+        
 
-        using (sb.BeginTargetTypeDeclare())
+        using (var typeDecl = sb.BeginTargetTypeDeclare())
         {
+            typeDecl.AddAttribute($"System.Runtime.CompilerServices.Union");
             GenerateTypeSpecifierEnumDeclaration(source);
 
             if (source.CandidateUnmanagedTypes.Length > 0)