diff --git a/dev/core/super/com/google/gwt/dev/jjs/intrinsic/com/google/gwt/lang/Cast.java b/dev/core/super/com/google/gwt/dev/jjs/intrinsic/com/google/gwt/lang/Cast.java
index fc9bcdb..df904e6 100644
--- a/dev/core/super/com/google/gwt/dev/jjs/intrinsic/com/google/gwt/lang/Cast.java
+++ b/dev/core/super/com/google/gwt/dev/jjs/intrinsic/com/google/gwt/lang/Cast.java
@@ -149,9 +149,12 @@
     // jso's typeId is undefined, because (undefined < positive int).
 
     if (jso && !(jso.@java.lang.Object::typeId >= _.@java.lang.Object::typeId)) {
+      // don't clobber toString
+      var oldToString = jso.toString;
       for (var i in _) {
         jso[i] = _[i];
       }
+      jso.toString = oldToString;
     }
     return jso;
   }-*/;