diff -r d382dacfd73f -r 00ae3f46e54f rt/emul/mini/src/main/java/java/lang/Throwable.java
--- a/rt/emul/mini/src/main/java/java/lang/Throwable.java	Tue Feb 26 16:54:16 2013 +0100
+++ b/rt/emul/mini/src/main/java/java/lang/Throwable.java	Fri Apr 26 13:35:21 2013 +0200
@@ -1085,4 +1085,22 @@
 //        else
 //            return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
     }
+    
+    private static Object bck2BrwsrCnvrt(Object o) {
+        if (o instanceof Throwable) {
+            return o;
+        }
+        final String msg = msg(o);
+        if (msg == null || msg.startsWith("TypeError")) {
+            return new NullPointerException(msg);
+        }
+        return new Throwable(msg);
+    }
+    
+    @JavaScriptBody(args = { "o" }, body = "return o ? o.toString() : null;")
+    private static native String msg(Object o);
+
+    @JavaScriptOnly(name = "bck2BrwsrCnvrt", value = "c.bck2BrwsrCnvrt__Ljava_lang_Object_2Ljava_lang_Object_2")
+    private static void bck2BrwsrCnvrtVM() {
+    }
 }