diff --git a/db/concurrency.h b/db/concurrency.h
index fcf41226ad1..d153862aa88 100644
--- a/db/concurrency.h
+++ b/db/concurrency.h
@@ -65,7 +65,7 @@ namespace mongo {
                 _state.set(s+1);
                 return;
             }
-            assert( s == 0 );
+            massert("internal error: locks are not upgradeable", s == 0 );
             _state.set(1);
             _m.lock(); 
             _minfo.entered();