diff --git a/xpcom/base/nsAgg.h b/xpcom/base/nsAgg.h
index 6c5fe76859eb..f9cf4050eb3a 100644
--- a/xpcom/base/nsAgg.h
+++ b/xpcom/base/nsAgg.h
@@ -143,8 +143,7 @@ _class::Internal::AddRef(void)                                              \
 {                                                                           \
     _class* agg = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Downcast(this);    \
     MOZ_ASSERT(int32_t(agg->mRefCnt) >= 0, "illegal refcnt");               \
-    NS_CheckThreadSafe(agg->_mOwningThread.GetThread(),                     \
-                       #_class " not thread-safe");                         \
+    NS_ASSERT_OWNINGTHREAD_AGGREGATE(agg, _class);                          \
     nsrefcnt count = agg->mRefCnt.incr();                                   \
     NS_LOG_ADDREF(this, count, #_class, sizeof(*agg));                      \
     return count;                                                           \
@@ -154,8 +153,7 @@ _class::Internal::Release(void)                                             \
 {                                                                           \
     _class* agg = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Downcast(this);    \
     MOZ_ASSERT(int32_t(agg->mRefCnt) > 0, "dup release");                   \
-    NS_CheckThreadSafe(agg->_mOwningThread.GetThread(),                     \
-                       #_class " not thread-safe");                         \
+    NS_ASSERT_OWNINGTHREAD_AGGREGATE(agg, _class);                          \
     nsrefcnt count = agg->mRefCnt.decr(this);                               \
     NS_LOG_RELEASE(this, count, #_class);                                   \
     return count;                                                           \
diff --git a/xpcom/glue/nsISupportsImpl.h b/xpcom/glue/nsISupportsImpl.h
index 9450d7d58e68..932cd15cc30e 100644
--- a/xpcom/glue/nsISupportsImpl.h
+++ b/xpcom/glue/nsISupportsImpl.h
@@ -61,11 +61,13 @@ private:
 };
 
 #define NS_DECL_OWNINGTHREAD            nsAutoOwningThread _mOwningThread;
-#define NS_ASSERT_OWNINGTHREAD(_class) \
-  NS_CheckThreadSafe(_mOwningThread.GetThread(), #_class " not thread-safe")
+#define NS_ASSERT_OWNINGTHREAD_AGGREGATE(agg, _class) \
+  NS_CheckThreadSafe(agg->_mOwningThread.GetThread(), #_class " not thread-safe")
+#define NS_ASSERT_OWNINGTHREAD(_class) NS_ASSERT_OWNINGTHREAD_AGGREGATE(this, _class)
 #else // !DEBUG && !NIGHTLY_BUILD
 
 #define NS_DECL_OWNINGTHREAD            /* nothing */
+#define NS_ASSERT_OWNINGTHREAD_AGGREGATE(agg, _class) ((void)0)
 #define NS_ASSERT_OWNINGTHREAD(_class)  ((void)0)
 
 #endif // DEBUG || NIGHTLY_BUILD