diff --git a/modules/libpref/public/nsIPref.idl b/modules/libpref/public/nsIPref.idl
index 3382db645d71..bd9b959f23af 100644
--- a/modules/libpref/public/nsIPref.idl
+++ b/modules/libpref/public/nsIPref.idl
@@ -39,6 +39,8 @@ typedef void (*PrefEnumerationFunc)(const char *, void *);
 
 #define NS_PREF_PROGID \
   "component://netscape/preferences" 
+
+#define NS_PREF_CLASSNAME "Preferences Service"
  
 #define NS_PREF_VALUE_CHANGED 1 
 %}