Index: sql/sql_select.cc
===================================================================
--- sql/sql_select.cc	(revision 25792)
+++ sql/sql_select.cc	(revision 25793)
@@ -13964,7 +13964,8 @@
             if (best_key < 0 ||
                 (select_limit <= min(quick_records,best_records) ?
                  keyinfo->key_parts < best_key_parts :
-                 quick_records < best_records))
+                 quick_records < best_records) ||
+                (quick_records == best_records && !is_best_covering && is_covering)) 
             {
               best_key= nr;
               best_key_parts= keyinfo->key_parts;