diff --git a/mysys/my_handler.c b/mysys/my_handler.c
index dd35fae251f..3bac59f409c 100644
--- a/mysys/my_handler.c
+++ b/mysys/my_handler.c
@@ -502,7 +502,7 @@ HA_KEYSEG *ha_find_null(HA_KEYSEG *keyseg, const uchar *a)
 {
   for (; (enum ha_base_keytype) keyseg->type != HA_KEYTYPE_END; keyseg++)
   {
-    uchar *end;
+    const uchar *end;
     if (keyseg->null_bit)
     {
       if (!*a++)