diff --git a/sql/sql_base.cc b/sql/sql_base.cc

index 2b06cf27d9b..93ed007300a 100644

--- a/sql/sql_base.cc

+++ b/sql/sql_base.cc

@@ -7503,6 +7503,10 @@ bool setup_fields(THD *thd, Ref_ptr_array ref_pointer_array,

   thd->column_usage= column_usage;

   DBUG_PRINT("info", ("thd->column_usage: %d", thd->column_usage));

+  DBUG_ASSERT(thd->lex->current_select->nest_level >= 0);

+  DBUG_ASSERT(thd->lex->current_select->master_unit()->first_select()

+                ->nest_level ==

+              thd->lex->current_select->nest_level);

   if (allow_sum_func)

     thd->lex->allow_sum_func.set_bit(thd->lex->current_select->nest_level);

   thd->where= THD::DEFAULT_WHERE;