diff --git a/cast128.c b/cast128.c
index a2b04d745245e7a49cd04dfccc6f69ae8a521d45..75783e5dd753addee9df20bf4190b31a4a7860e0 100644
--- a/cast128.c
+++ b/cast128.c
@@ -1,6 +1,6 @@
 /* cast128.c
  *
- * The CAST-128 block cipher.
+ * The CAST-128 block cipher, described in RFC 2144.
  */
 
 /*	CAST-128 in C