diff --git a/sql/item_windowfunc.cc b/sql/item_windowfunc.cc
index 5438cade27a..a770caa2222 100644
--- a/sql/item_windowfunc.cc
+++ b/sql/item_windowfunc.cc
@@ -124,7 +124,8 @@ Item_window_func::fix_fields(THD *thd, Item **ref)
 
   const_item_cache= false;
 
-  with_flags= (with_flags & ~item_with_t::SUM_FUNC) | item_with_t::WINDOW_FUNC;
+  DBUG_ASSERT((bool) (with_flags & item_with_t::WINDOW_FUNC));
+  with_flags&= ~item_with_t::SUM_FUNC;
 
   if (fix_length_and_dec(thd))
     return TRUE;
diff --git a/sql/item_windowfunc.h b/sql/item_windowfunc.h
index 8d78282d982..923732b4501 100644
--- a/sql/item_windowfunc.h
+++ b/sql/item_windowfunc.h
@@ -1086,13 +1086,19 @@ public:
     : Item_func_or_sum(thd, (Item *) win_func),
       window_name(win_name), window_spec(NULL), 
       force_return_blank(true),
-      read_value_from_result_field(false) {}
+      read_value_from_result_field(false)
+  {
+    with_flags|= item_with_t::WINDOW_FUNC;
+  }
 
   Item_window_func(THD *thd, Item_sum *win_func, Window_spec *win_spec)
     : Item_func_or_sum(thd, (Item *) win_func), 
       window_name(NULL), window_spec(win_spec), 
       force_return_blank(true),
-      read_value_from_result_field(false) {}
+      read_value_from_result_field(false)
+  {
+    with_flags|= item_with_t::WINDOW_FUNC;
+  }
 
   Item_sum *window_func() const { return (Item_sum *) args[0]; }