diff --git a/csharp/src/Google.Protobuf.Test.TestProtos/UnittestIssues.cs b/csharp/src/Google.Protobuf.Test.TestProtos/UnittestIssues.cs
index e7aaacea553d..e09191a65cec 100644
--- a/csharp/src/Google.Protobuf.Test.TestProtos/UnittestIssues.cs
+++ b/csharp/src/Google.Protobuf.Test.TestProtos/UnittestIssues.cs
@@ -3016,6 +3016,9 @@ public enum ValueOneofCase {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void WriteTo(pb::CodedOutputStream output) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      output.WriteRawMessage(this);
+    #else
       if (valueCase_ == ValueOneofCase.StringValue) {
         output.WriteRawTag(10);
         output.WriteString(StringValue);
@@ -3027,7 +3030,25 @@ public enum ValueOneofCase {
       if (_unknownFields != null) {
         _unknownFields.WriteTo(output);
       }
+    #endif
+    }
+
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    void pb::IBufferMessage.InternalWriteTo(ref pb::WriteContext output) {
+      if (valueCase_ == ValueOneofCase.StringValue) {
+        output.WriteRawTag(10);
+        output.WriteString(StringValue);
+      }
+      if (valueCase_ == ValueOneofCase.NullValue) {
+        output.WriteRawTag(16);
+        output.WriteEnum((int) NullValue);
+      }
+      if (_unknownFields != null) {
+        _unknownFields.WriteTo(ref output);
+      }
     }
+    #endif
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public int CalculateSize() {
@@ -3194,6 +3215,9 @@ public sealed partial class NullValueNotInOneof : pb::IMessage<NullValueNotInOne
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void WriteTo(pb::CodedOutputStream output) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      output.WriteRawMessage(this);
+    #else
       if (NullValue != global::Google.Protobuf.WellKnownTypes.NullValue.NullValue) {
         output.WriteRawTag(16);
         output.WriteEnum((int) NullValue);
@@ -3201,8 +3225,22 @@ public sealed partial class NullValueNotInOneof : pb::IMessage<NullValueNotInOne
       if (_unknownFields != null) {
         _unknownFields.WriteTo(output);
       }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    void pb::IBufferMessage.InternalWriteTo(ref pb::WriteContext output) {
+      if (NullValue != global::Google.Protobuf.WellKnownTypes.NullValue.NullValue) {
+        output.WriteRawTag(16);
+        output.WriteEnum((int) NullValue);
+      }
+      if (_unknownFields != null) {
+        _unknownFields.WriteTo(ref output);
+      }
+    }
+    #endif
+
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public int CalculateSize() {
       int size = 0;