diff --git a/sql/sql_help.cc b/sql/sql_help.cc
index ff2f5bf4992..759b535da53 100644
--- a/sql/sql_help.cc
+++ b/sql/sql_help.cc
@@ -558,6 +558,10 @@ SQL_SELECT *prepare_simple_select(THD *thd, Item *cond, TABLE_LIST *tables,
 {
   if (!cond->fixed)
     cond->fix_fields(thd, tables, &cond);	// can never fail
+
+  /* Assume that no indexes cover all required fields */
+  table->used_keys.clear_all();
+
   SQL_SELECT *res= make_select(table,0,0,cond,error);
   if (*error || (res && res->check_quick(thd, 0, HA_POS_ERROR)) ||
       (res->quick && res->quick->reset()))