diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator.Shapes/Shapes/Shape.cs b/Appegy.Union.Generator~/Appegy.Union.Generator.Shapes/Shapes/Shape.cs
index 0e80025..cb510cb 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator.Shapes/Shapes/Shape.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator.Shapes/Shapes/Shape.cs
@@ -1,4 +1,6 @@
-namespace Appegy.Union.Generator.Shapes;
+using System.Runtime.InteropServices;
+
+namespace Appegy.Union.Generator.Shapes;
 
 public interface IShape
 {
@@ -7,4 +9,5 @@ public interface IShape
 
 [Union(typeof(Circle), typeof(Rectangle), typeof(Hexagon))]
 [Expose(typeof(IShape))]
+[StructLayout(LayoutKind.Explicit, Pack = 1)]
 public partial struct Shape;
\ No newline at end of file
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionComparisonPart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionComparisonPart.cs
index 9c96e8f..95c7b39 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionComparisonPart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionComparisonPart.cs
@@ -6,7 +6,8 @@ public class UnionComparisonPart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (syntax, types) = input;
+        var syntax = input.Syntax;
+        var types = input.Types;
 
         codeWriter.Write("public static bool operator ==(");
         codeWriter.Write(syntax.Identifier.Text);
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionConstructorsPart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionConstructorsPart.cs
index fce1ca4..12a57f9 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionConstructorsPart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionConstructorsPart.cs
@@ -7,7 +7,8 @@ public class UnionConstructorsPart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (syntax, types) = input;
+        var syntax = input.Syntax;
+        var types = input.Types;
 
         for (var i = 0; i < types.Count; i++)
         {
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionDeclarationPart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionDeclarationPart.cs
index e22ad2e..653a00d 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionDeclarationPart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionDeclarationPart.cs
@@ -6,10 +6,10 @@ public class UnionDeclarationPart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (syntax, types) = input;
+        var syntax = input.Syntax;
+        var types = input.Types;
 
         codeWriter.WriteLine(AttributesNames.GeneratedCodeAttribute);
-        codeWriter.WriteLine("[global::System.Runtime.InteropServices.StructLayout(global::System.Runtime.InteropServices.LayoutKind.Explicit, Pack = 1)]");
         codeWriter.Write("partial struct ");
         codeWriter.WriteLine(syntax.Identifier.Text);
 
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionEqualsPart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionEqualsPart.cs
index b1de4ab..335f88a 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionEqualsPart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionEqualsPart.cs
@@ -6,7 +6,8 @@ public class UnionEqualsPart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (syntax, types) = input;
+        var syntax = input.Syntax;
+        var types = input.Types;
 
         codeWriter.WriteLine("public override bool Equals(object boxed) => boxed switch");
         codeWriter.WriteLine('{');
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionFieldsPart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionFieldsPart.cs
index 86b2629..2cfdc67 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionFieldsPart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionFieldsPart.cs
@@ -6,14 +6,21 @@ public class UnionFieldsPart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (_, types) = input;
+        var types = input.Types;
+        var explicitLayout = input.ExplicitLayout;
 
-        codeWriter.WriteLine("[global::System.Runtime.InteropServices.FieldOffset(0)]");
+        if (explicitLayout)
+        {
+            codeWriter.WriteLine("[global::System.Runtime.InteropServices.FieldOffset(0)]");
+        }
         codeWriter.WriteLine("private Kind _type;");
 
         foreach (var type in types)
         {
-            codeWriter.WriteLine("[global::System.Runtime.InteropServices.FieldOffset(1)]");
+            if (explicitLayout)
+            {
+                codeWriter.WriteLine("[global::System.Runtime.InteropServices.FieldOffset(1)]");
+            }
             codeWriter.Write("private ");
             codeWriter.Write(type.FullName);
             codeWriter.Write(' ');
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionGetHashCodePart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionGetHashCodePart.cs
index e701f07..e0f3a8b 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionGetHashCodePart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionGetHashCodePart.cs
@@ -6,7 +6,7 @@ public class UnionGetHashCodePart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (_, types) = input;
+        var types = input.Types;
 
         codeWriter.WriteLine("public override int GetHashCode() => _type switch");
         codeWriter.WriteLine('{');
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionOperatorsPart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionOperatorsPart.cs
index eb81c47..e7a253a 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionOperatorsPart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionOperatorsPart.cs
@@ -6,7 +6,8 @@ public class UnionOperatorsPart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (syntax, types) = input;
+        var syntax = input.Syntax;
+        var types = input.Types;
 
         for (var i = 0; i < types.Count; i++)
         {
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionPropertiesPart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionPropertiesPart.cs
index e62589c..288d1eb 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionPropertiesPart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionPropertiesPart.cs
@@ -1,5 +1,4 @@
 using System.CodeDom.Compiler;
-using SymbolDisplayFormat = Microsoft.CodeAnalysis.SymbolDisplayFormat;
 
 namespace Appegy.Union.Generator;
 
@@ -7,7 +6,7 @@ public class UnionPropertiesPart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (_, types) = input;
+        var types = input.Types;
 
         codeWriter.WriteLine("public Kind Type => _type;");
         codeWriter.WriteLine();
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionToStringPart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionToStringPart.cs
index e896cdb..3d6765d 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionToStringPart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionToStringPart.cs
@@ -6,7 +6,7 @@ public class UnionToStringPart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (_, types) = input;
+        var types = input.Types;
 
         codeWriter.WriteLine("public override string ToString() => _type switch");
         codeWriter.WriteLine('{');
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionTypeEnumPart.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionTypeEnumPart.cs
index 63e3cc9..72cb116 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionTypeEnumPart.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/Parts/UnionTypeEnumPart.cs
@@ -6,7 +6,7 @@ public class UnionTypeEnumPart : GeneratorPart<UnionAttributePartInput>
 {
     public override void Generate(IndentedTextWriter codeWriter, UnionAttributePartInput input)
     {
-        var (_, types) = input;
+        var types = input.Types;
 
         codeWriter.WriteLine("[global::System.Serializable]");
         codeWriter.WriteLine("public enum Kind : global::System.Byte");
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/UnionAttributeGenerator.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/UnionAttributeGenerator.cs
index 9700817..81e9d92 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/UnionAttributeGenerator.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/UnionAttributeGenerator.cs
@@ -44,17 +44,21 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
                 transform: static (ctx, _) =>
                 {
                     var syntax = (StructDeclarationSyntax)ctx.TargetNode;
+                    var symbol = ctx.SemanticModel.GetDeclaredSymbol(syntax);
                     var attribute = ctx.Attributes.First();
                     var types = attribute
                         .GetTypesFromConstructor(TypeKind.Struct)
                         .Select(c => new UnionTypeInfo(c))
                         .ToImmutableList();
-                    return (syntax, types);
+
+                    var explicitLayout = HasExplicitStructLayoutAttribute(symbol);
+
+                    return (syntax, types, explicitLayout);
                 });
 
         context.RegisterSourceOutput(sources, static (ctx, input) =>
         {
-            var (syntax, types) = input;
+            var (syntax, types, explicitLayout) = input;
 
             if (!syntax.Modifiers.Any(SyntaxKind.PartialKeyword)) return;
             if (types.Count == 0) return;
@@ -63,10 +67,36 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
             using var streamWriter = new StreamWriter(memoryStream, Encoding.UTF8);
             using var codeWriter = new IndentedTextWriter(streamWriter, "    ");
 
-            codeWriter.AppendParts(Parts, new UnionAttributePartInput(syntax, types));
+            codeWriter.AppendParts(Parts, new UnionAttributePartInput(syntax, types, explicitLayout));
 
             streamWriter.Flush();
             ctx.AddSource($"{syntax.Identifier.Text}_Union.g.cs", SourceText.From(memoryStream, Encoding.UTF8, canBeEmbedded: true));
         });
     }
+
+    private static bool HasExplicitStructLayoutAttribute(INamedTypeSymbol? symbol)
+    {
+        if (symbol == null) return false;
+
+        return symbol.GetAttributes().Any(attr =>
+        {
+            if (attr.AttributeClass?.Name != "StructLayoutAttribute" ||
+                attr.AttributeClass.ContainingNamespace?.ToDisplayString() != "System.Runtime.InteropServices")
+            {
+                return false;
+            }
+
+            if (attr.ConstructorArguments.Length > 0)
+            {
+                var layoutKindArg = attr.ConstructorArguments[0];
+
+                if (layoutKindArg.Type?.Name == "LayoutKind" && layoutKindArg.Type.ContainingNamespace?.ToDisplayString() == "System.Runtime.InteropServices")
+                {
+                    return layoutKindArg.Value is 2;
+                }
+            }
+
+            return false;
+        });
+    }
 }
\ No newline at end of file
diff --git a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/UnionAttributePartInput.cs b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/UnionAttributePartInput.cs
index 8475807..83ca80b 100644
--- a/Appegy.Union.Generator~/Appegy.Union.Generator/Union/UnionAttributePartInput.cs
+++ b/Appegy.Union.Generator~/Appegy.Union.Generator/Union/UnionAttributePartInput.cs
@@ -4,7 +4,7 @@
 
 namespace Appegy.Union.Generator;
 
-public record struct UnionAttributePartInput(StructDeclarationSyntax Syntax, IReadOnlyList<UnionTypeInfo> Types);
+public record struct UnionAttributePartInput(StructDeclarationSyntax Syntax, IReadOnlyList<UnionTypeInfo> Types, bool ExplicitLayout);
 
 public readonly struct UnionTypeInfo(INamedTypeSymbol symbol)
 {
diff --git a/Runtime/Appegy.Union.Generator.dll b/Runtime/Appegy.Union.Generator.dll
index 2f522f7..3d1d07a 100644
--- a/Runtime/Appegy.Union.Generator.dll
+++ b/Runtime/Appegy.Union.Generator.dll
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:d1141df8050ec5086c10e75ac2e0047630095079b1707cbe1e61f6500574e597
-size 55296
+oid sha256:8f674aa7f435e096cf702b4424fecc8de7c7a6fcdb162f2f1dd4b8fe1dcadbd2
+size 55808
diff --git a/Runtime/Appegy.Union.Generator.pdb b/Runtime/Appegy.Union.Generator.pdb
index a10f83c..775af18 100644
Binary files a/Runtime/Appegy.Union.Generator.pdb and b/Runtime/Appegy.Union.Generator.pdb differ