diff --git a/js/xpconnect/src/xpcprivate.h b/js/xpconnect/src/xpcprivate.h
index 8a86ebf2c7c..b576bbdfb52 100644
--- a/js/xpconnect/src/xpcprivate.h
+++ b/js/xpconnect/src/xpcprivate.h
@@ -1310,12 +1310,13 @@ public:
     XPCCallContext &GetXPCCallContext()
     {
         if (!mCcx) {
+            XPCCallContext *data = mData.addr();
             mCcxToDestroy = mCcx =
-                new (mData) XPCCallContext(mCallerLanguage, mCx,
-                                           mCallBeginRequest == CALL_BEGINREQUEST,
-                                           mObj,
-                                           mFlattenedJSObject, mWrapper,
-                                           mTearOff);
+                new (data) XPCCallContext(mCallerLanguage, mCx,
+                                          mCallBeginRequest == CALL_BEGINREQUEST,
+                                          mObj,
+                                          mFlattenedJSObject, mWrapper,
+                                          mTearOff);
             if (!mCcx->IsValid()) {
                 NS_ERROR("This is not supposed to fail!");
             }
@@ -1343,7 +1344,7 @@ private:
     JSObject *mFlattenedJSObject;
     XPCWrappedNative *mWrapper;
     XPCWrappedNativeTearOff *mTearOff;
-    char mData[sizeof(XPCCallContext)];
+    mozilla::AlignedStorage2<XPCCallContext> mData;
 };
 
 /***************************************************************************