--- a/xpcom/base/CycleCollectedJSContext.h
+++ b/xpcom/base/CycleCollectedJSContext.h
@@ -138,16 +138,17 @@ class CycleCollectedJSContext
 {
   friend class JSGCThingParticipant;
   friend class JSZoneParticipant;
   friend class IncrementalFinalizeRunnable;
 protected:
   CycleCollectedJSContext();
   virtual ~CycleCollectedJSContext();
 
+  MOZ_IS_CLASS_INIT
   nsresult Initialize(JSContext* aParentContext,
                       uint32_t aMaxBytes,
                       uint32_t aMaxNurseryBytes);
 
   size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
   void UnmarkSkippableJSHolders();
 
   virtual void