diff --git a/appl/popper/pop_msg.c b/appl/popper/pop_msg.c
index e30afb657..a197a41db 100644
--- a/appl/popper/pop_msg.c
+++ b/appl/popper/pop_msg.c
@@ -12,7 +12,7 @@ RCSID("$Id$");
  */
 
 int
-pop_msg(POP *p, int stat, char *format, ...)
+pop_msg(POP *p, int stat, const char *format, ...)
 {
     char	       *mp;
     char                message[MAXLINELEN];