diff --git a/lib/log.c b/lib/log.c
index f7a3685..8c3e2dd 100644
--- a/lib/log.c
+++ b/lib/log.c
@@ -771,7 +771,7 @@
  * provided otherwise.
  */
 const char *
-mes_lookup (struct message *meslist, int max, int index, const char *none)
+mes_lookup (const struct message *meslist, int max, int index, const char *none)
 {
   int pos = index - meslist[0].key;