diff --git a/src/base/fttrigon.c b/src/base/fttrigon.c
index 4ffdcb77f..e3ce8a6d0 100644
--- a/src/base/fttrigon.c
+++ b/src/base/fttrigon.c
@@ -111,6 +111,7 @@
 #endif /* !FT_LONG64 */
 
 
+  /* undefined and never called for zero vector */  
   static FT_Int
   ft_trig_prenorm( FT_Vector*  vec )
   {