diff --git a/src/ProtocolBuffers.Test/GeneratedMessageTest.cs b/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
index 80923ca..610078f 100644
--- a/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
+++ b/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
@@ -385,5 +385,13 @@
       Assert.IsTrue(builder.IsInitialized);
       Assert.IsTrue(builder.BuildPartial().IsInitialized);
     }
+
+    [Test]
+    public void ToBuilder() {
+      TestAllTypes.Builder builder = TestAllTypes.CreateBuilder();
+      TestUtil.SetAllFields(builder);
+      TestAllTypes message = builder.Build();
+      TestUtil.AssertAllFieldsSet(message.ToBuilder().Build());
+    }
   }
 }