diff --git a/mozilla/content/events/src/nsEventListenerManager.cpp b/mozilla/content/events/src/nsEventListenerManager.cpp
index 5af2eda0227..6597d3a14fa 100644
--- a/mozilla/content/events/src/nsEventListenerManager.cpp
+++ b/mozilla/content/events/src/nsEventListenerManager.cpp
@@ -826,6 +826,10 @@ nsEventListenerManager::AddScriptEventListener(nsISupports *aObject,
                                           aBody,
                                           url.get(), lineNo,
                                           handler);
+        if (rv == NS_ERROR_ILLEGAL_VALUE) {
+          NS_WARNING("Probably a syntax error in the event handler!");
+          return NS_SUCCESS_LOSS_OF_INSIGNIFICANT_DATA;
+        }
         NS_ENSURE_SUCCESS(rv, rv);
         // And bind it.
         rv = context->BindCompiledEventHandler(aObject, scope,
diff --git a/mozilla/dom/src/base/nsJSEnvironment.cpp b/mozilla/dom/src/base/nsJSEnvironment.cpp
index 27b5e4301d2..73027f51301 100644
--- a/mozilla/dom/src/base/nsJSEnvironment.cpp
+++ b/mozilla/dom/src/base/nsJSEnvironment.cpp
@@ -1671,7 +1671,7 @@ nsJSContext::CompileEventHandler(nsIAtom *aName,
                                           aURL, aLineNo);
 
   if (!fun) {
-    return NS_ERROR_FAILURE;
+    return NS_ERROR_ILLEGAL_VALUE;
   }
 
   JSObject *handler = ::JS_GetFunctionObject(fun);