diff --git a/mozilla/xpcom/ds/nsDoubleHashtable.h b/mozilla/xpcom/ds/nsDoubleHashtable.h
index 381f322ac8f..3f89fd77c59 100644
--- a/mozilla/xpcom/ds/nsDoubleHashtable.h
+++ b/mozilla/xpcom/ds/nsDoubleHashtable.h
@@ -48,7 +48,7 @@ class nsISupports;
  *
  * A hashtable from string -> nsISupports*.  Holds strong references.
  */
-class nsDoubleHashtableStringSupports {
+class NS_COM nsDoubleHashtableStringSupports {
 public:
   nsDoubleHashtableStringSupports();
   ~nsDoubleHashtableStringSupports();