diff --git a/sql/opt_range.cc b/sql/opt_range.cc
index 27ea4a83714..1b4f20bc39c 100644
--- a/sql/opt_range.cc
+++ b/sql/opt_range.cc
@@ -7171,7 +7171,7 @@ SEL_TREE *Item_func_in::get_func_mm_tree(RANGE_OPT_PARAM *param,
       {
         key_map::Iterator it(field->key_start);
         uint key_no;
-        while ((key_no= it.next_bit()) != key_map::Iterator::BITMAP_END)
+        while ((key_no= it++) != key_map::Iterator::BITMAP_END)
         {
           KEY *key_info= &field->table->key_info[key_no];
           if (key_info->user_defined_key_parts == 1 &&