--- a/dom/src/base/nsJSTimeoutHandler.cpp
+++ b/dom/src/base/nsJSTimeoutHandler.cpp
@@ -233,25 +233,27 @@ nsJSScriptTimeoutHandler::Init(nsIScript
   int32 interval = 0;
 
   JSAutoRequest ar(cx);
 
   if (argc < 1) {
     ::JS_ReportError(cx, "Function %s requires at least 1 parameter",
                      aIsInterval ? kSetIntervalStr : kSetTimeoutStr);
 
-    return ncc->SetExceptionWasThrown(PR_TRUE);
+    ncc->SetExceptionWasThrown(PR_TRUE);
+    return NS_ERROR_DOM_TYPE_ERR;
   }
 
   if (argc > 1 && !::JS_ValueToECMAInt32(cx, argv[1], &interval)) {
     ::JS_ReportError(cx,
                      "Second argument to %s must be a millisecond interval",
                      aIsInterval ? kSetIntervalStr : kSetTimeoutStr);
 
-    return ncc->SetExceptionWasThrown(PR_TRUE);
+    ncc->SetExceptionWasThrown(PR_TRUE);
+    return NS_ERROR_DOM_TYPE_ERR;
   }
 
   switch (::JS_TypeOfValue(cx, argv[0])) {
   case JSTYPE_FUNCTION:
     funobj = JSVAL_TO_OBJECT(argv[0]);
     break;
 
   case JSTYPE_STRING: