diff --git a/lib/delphi/src/Thrift.Protocol.pas b/lib/delphi/src/Thrift.Protocol.pas
index 7ff2eae..9ea28de 100644
--- a/lib/delphi/src/Thrift.Protocol.pas
+++ b/lib/delphi/src/Thrift.Protocol.pas
@@ -823,7 +823,7 @@
     end;
 
   else
-    ASSERT( FALSE); // any new types?
+    raise TProtocolExceptionInvalidData.Create('Unexpected type '+IntToStr(Ord(type_)));
   end;
 end;