diff --git a/js/src/xpconnect/src/xpcprivate.h b/js/src/xpconnect/src/xpcprivate.h
index 86cbf61ca646..6f20f0cccad6 100644
--- a/js/src/xpconnect/src/xpcprivate.h
+++ b/js/src/xpconnect/src/xpcprivate.h
@@ -4030,7 +4030,7 @@ public:
      * @param errorReporter the error reporter callback function to set
      */
 
-    void StartEvaluating(JSErrorReporter errorReporter = nsnull);
+    PRBool StartEvaluating(JSObject *scope, JSErrorReporter errorReporter = nsnull);
     /**
      * Does the post script evaluation and resets the error reporter
      */
@@ -4041,6 +4041,7 @@ private:
     PRBool mErrorReporterSet;
     PRBool mEvaluated;
     jsword mContextHasThread;
+    JSAutoEnterCompartment mEnterCompartment;
     MOZILLA_DECL_USE_GUARD_OBJECT_NOTIFIER
 
     // No copying or assignment allowed
diff --git a/js/src/xpconnect/src/xpcwrappedjsclass.cpp b/js/src/xpconnect/src/xpcwrappedjsclass.cpp
index 8e8736d8975b..1626f027e2b1 100644
--- a/js/src/xpconnect/src/xpcwrappedjsclass.cpp
+++ b/js/src/xpconnect/src/xpcwrappedjsclass.cpp
@@ -54,12 +54,13 @@ NS_IMPL_THREADSAFE_ISUPPORTS1(nsXPCWrappedJSClass, nsIXPCWrappedJSClass)
 // the value of this variable is never used - we use its address as a sentinel
 static uint32 zero_methods_descriptor;
 
-void AutoScriptEvaluate::StartEvaluating(JSErrorReporter errorReporter)
+PRBool AutoScriptEvaluate::StartEvaluating(JSObject *scope, JSErrorReporter errorReporter)
 {
     NS_PRECONDITION(!mEvaluated, "AutoScriptEvaluate::Evaluate should only be called once");
 
-    if(!mJSContext)
-        return;
+    if (!mJSContext)
+        return PR_TRUE;
+
     mEvaluated = PR_TRUE;
     if(!mJSContext->errorReporter)
     {
@@ -70,6 +71,9 @@ void AutoScriptEvaluate::StartEvaluating(JSErrorReporter errorReporter)
     if (mContextHasThread)
         JS_BeginRequest(mJSContext);
 
+    if (!mEnterCompartment.enter(mJSContext, scope))
+        return PR_FALSE;
+
     // Saving the exception state keeps us from interfering with another script
     // that may also be running on this context.  This occurred first with the
     // js debugger, as described in
@@ -85,6 +89,8 @@ void AutoScriptEvaluate::StartEvaluating(JSErrorReporter errorReporter)
         mState = JS_SaveExceptionState(mJSContext);
         JS_ClearPendingException(mJSContext);
     }
+
+    return PR_TRUE;
 }
 
 AutoScriptEvaluate::~AutoScriptEvaluate()
@@ -250,10 +256,6 @@ nsXPCWrappedJSClass::CallQueryInterfaceOnJSObject(XPCCallContext& ccx,
     JSBool success = JS_FALSE;
     jsid funid;
     jsval fun;
-    JSAutoEnterCompartment ac;
-
-    if(!ac.enter(cx, jsobj))
-        return nsnull;
 
     // Don't call the actual function on a content object. We'll determine
     // whether or not a content object is capable of implementing the
@@ -265,6 +267,14 @@ nsXPCWrappedJSClass::CallQueryInterfaceOnJSObject(XPCCallContext& ccx,
         return nsnull;
     }
 
+    // OK, it looks like we'll be calling into JS code.
+    AutoScriptEvaluate scriptEval(cx);
+
+    // XXX we should install an error reporter that will send reports to
+    // the JS error console service.
+    if (!scriptEval.StartEvaluating(jsobj))
+        return nsnull;
+
     // check upfront for the existence of the function property
     funid = mRuntime->GetStringID(XPCJSRuntime::IDX_QUERY_INTERFACE);
     if(!JS_GetPropertyById(cx, jsobj, funid, &fun) || JSVAL_IS_PRIMITIVE(fun))
@@ -290,14 +300,6 @@ nsXPCWrappedJSClass::CallQueryInterfaceOnJSObject(XPCCallContext& ccx,
             return nsnull;
     }
 
-    // OK, it looks like we'll be calling into JS code.
-
-    AutoScriptEvaluate scriptEval(cx);
-
-    // XXX we should install an error reporter that will send reports to
-    // the JS error console service.
-    scriptEval.StartEvaluating();
-
     id = xpc_NewIDObject(cx, jsobj, aIID);
     if(id)
     {
@@ -402,7 +404,8 @@ nsXPCWrappedJSClass::GetNamedPropertyAsVariant(XPCCallContext& ccx,
     nsresult rv = NS_ERROR_FAILURE;
 
     AutoScriptEvaluate scriptEval(cx);
-    scriptEval.StartEvaluating();
+    if (!scriptEval.StartEvaluating(aJSObj))
+        return NS_ERROR_FAILURE;
 
     ok = JS_ValueToId(cx, aName, &id) && 
          GetNamedPropertyAsVariantRaw(ccx, aJSObj, id, aResult, &rv);
@@ -425,7 +428,8 @@ nsXPCWrappedJSClass::BuildPropertyEnumerator(XPCCallContext& ccx,
 
     // Saved state must be restored, all exits through 'out'...
     AutoScriptEvaluate scriptEval(cx);
-    scriptEval.StartEvaluating();
+    if (!scriptEval.StartEvaluating(aJSObj))
+        return NS_ERROR_FAILURE;
 
     idArray = JS_Enumerate(cx, aJSObj);
     if(!idArray)
@@ -1306,16 +1310,11 @@ nsXPCWrappedJSClass::CallMethod(nsXPCWrappedJS* wrapper, uint16 methodIndex,
     }
 
     js::AutoValueVector args(cx);
-    /* This must come before AutoScriptEvaluate */
-    JSAutoEnterCompartment ac;
     AutoScriptEvaluate scriptEval(cx);
     ContextPrincipalGuard principalGuard(ccx);
 
     obj = thisObj = wrapper->GetJSObject();
 
-    if (!ac.enter(ccx, obj))
-        goto pre_call_clean_up;
-
     // XXX ASSUMES that retval is last arg. The xpidl compiler ensures this.
     paramCount = info->num_args;
     argc = paramCount -
@@ -1324,7 +1323,8 @@ nsXPCWrappedJSClass::CallMethod(nsXPCWrappedJS* wrapper, uint16 methodIndex,
     if(!cx || !xpcc || !IsReflectable(methodIndex))
         goto pre_call_clean_up;
 
-    scriptEval.StartEvaluating(xpcWrappedJSErrorReporter);
+    if (!scriptEval.StartEvaluating(obj, xpcWrappedJSErrorReporter))
+        goto pre_call_clean_up;
 
     xpcc->SetPendingResult(pending_result);
     xpcc->SetException(nsnull);