diff --git a/lib/log.h b/lib/log.h
index 8948ea0..defe064 100644
--- a/lib/log.h
+++ b/lib/log.h
@@ -71,7 +71,7 @@
 struct message
 {
   int key;
-  char *str;
+  const char *str;
 };
 
 /* Default logging strucutre. */