diff --git a/sql/item_sum.h b/sql/item_sum.h
index 5f2c4f166e6..c76f3102003 100644
--- a/sql/item_sum.h
+++ b/sql/item_sum.h
@@ -303,6 +303,8 @@ class st_select_lex;
 
 class Item_sum :public Item_result_field
 {
+  friend class Aggregator_distinct;
+
 protected:
   /**
     Aggregator class instance. Not set initially. Allocated only after