diff --git a/widget/nsGUIEvent.h b/widget/nsGUIEvent.h
index f77c18583104..06eb6468c9db 100644
--- a/widget/nsGUIEvent.h
+++ b/widget/nsGUIEvent.h
@@ -1076,7 +1076,8 @@ public:
     : nsInputEvent(isTrusted, msg, w, NS_KEY_EVENT),
       keyCode(0), charCode(0),
       location(nsIDOMKeyEvent::DOM_KEY_LOCATION_STANDARD), isChar(0),
-      mKeyNameIndex(mozilla::widget::KEY_NAME_INDEX_Unidentified)
+      mKeyNameIndex(mozilla::widget::KEY_NAME_INDEX_Unidentified),
+      mNativeKeyEvent(nullptr)
   {
   }
 
@@ -1093,6 +1094,8 @@ public:
   bool            isChar;
   // DOM KeyboardEvent.key
   mozilla::widget::KeyNameIndex mKeyNameIndex;
+  // OS-specific native event can optionally be preserved
+  void*           mNativeKeyEvent;
 
   void GetDOMKeyName(nsAString& aKeyName)
   {
diff --git a/widget/nsGUIEventIPC.h b/widget/nsGUIEventIPC.h
index 07dfc84ab89f..101bea524fb3 100644
--- a/widget/nsGUIEventIPC.h
+++ b/widget/nsGUIEventIPC.h
@@ -258,6 +258,8 @@ struct ParamTraits<nsKeyEvent>
     WriteParam(aMsg, aParam.charCode);
     WriteParam(aMsg, aParam.isChar);
     WriteParam(aMsg, aParam.location);
+    // An OS-specific native event might be attached in |mNativeKeyEvent|,  but
+    // that cannot be copied across process boundaries.
   }
 
   static bool Read(const Message* aMsg, void** aIter, paramType* aResult)