diff --git a/xpcom/macbuild/xpcom.exp b/xpcom/macbuild/xpcom.exp
index be5b8d07d2df..009a20558aa2 100644
--- a/xpcom/macbuild/xpcom.exp
+++ b/xpcom/macbuild/xpcom.exp
@@ -93,3 +93,9 @@ Destroy__13nsTraceRefcntFPvPCci
 Create__13nsTraceRefcntFPvPCcPCci
 Release__13nsTraceRefcntFPvUlPCci
 AddRef__13nsTraceRefcntFPvUlPCci
+
+# nsCOMPtr
+begin_assignment__13nsCOMPtr_baseFv
+assign_with_QueryInterface__13nsCOMPtr_baseFP11nsISupportsRC4nsIDPUi
+assign_with_AddRef__13nsCOMPtr_baseFP11nsISupports
+