diff --git a/src/ProtocolBuffers.Test/AbstractMessageTest.cs b/src/ProtocolBuffers.Test/AbstractMessageTest.cs
index e300ac9..f1dbda3 100644
--- a/src/ProtocolBuffers.Test/AbstractMessageTest.cs
+++ b/src/ProtocolBuffers.Test/AbstractMessageTest.cs
@@ -465,7 +465,7 @@
                     return this;
                 }
 
-                public override Builder MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry)
+                public override Builder MergeFrom(ICodedInputStream input, ExtensionRegistry extensionRegistry)
                 {
                     wrappedBuilder.WeakMergeFrom(input, extensionRegistry);
                     return this;