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;
   
diff --git a/lib/log.h b/lib/log.h
index 8609791..2dd1d31 100644
--- a/lib/log.h
+++ b/lib/log.h
@@ -151,7 +151,7 @@
 #define LOOKUP(x, y) mes_lookup(x, x ## _max, y, "(no item found)")
 
 extern const char *lookup (const struct message *, int);
-extern const char *mes_lookup (struct message *meslist, 
+extern const char *mes_lookup (const struct message *meslist, 
                                int max, int index,
                                const char *no_item);