diff --git a/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.Proto2.cs b/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.Proto2.cs
index 5f90c94..1abed60 100644
--- a/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.Proto2.cs
+++ b/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.Proto2.cs
@@ -344,6 +344,8 @@
                 }
             };
 
+            MessageParsingHelpers.AssertWritingMessage(message);
+
             MessageParsingHelpers.AssertRoundtrip(Proto2.TestAllTypes.Parser, message);
         }
 
@@ -359,6 +361,8 @@
                 new RepeatedGroup_extension { A = 30 }
             });
 
+            MessageParsingHelpers.AssertWritingMessage(message);
+
             MessageParsingHelpers.AssertRoundtrip(
                 TestAllExtensions.Parser.WithExtensionRegistry(new ExtensionRegistry() { UnittestExtensions.OptionalGroupExtension, UnittestExtensions.RepeatedGroupExtension }),
                 message);
@@ -370,6 +374,8 @@
             var message = new TestGroupExtension();
             message.SetExtension(TestNestedExtension.Extensions.OptionalGroupExtension, new TestNestedExtension.Types.OptionalGroup_extension { A = 10 });
 
+            MessageParsingHelpers.AssertWritingMessage(message);
+            
             MessageParsingHelpers.AssertRoundtrip(
                 TestGroupExtension.Parser.WithExtensionRegistry(new ExtensionRegistry() { TestNestedExtension.Extensions.OptionalGroupExtension }),
                 message);