diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index edd0006..3a79014 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -3874,7 +3874,8 @@ String *Item_func_quote::val_str(String *str) {
   if (!arg)  // Null argument
   {
     /* Return the string 'NULL' */
-    str->copy(STRING_WITH_LEN("NULL"), collation.collation);
+    str->set_charset(collation.collation);
+    str->set_ascii(STRING_WITH_LEN("NULL"));
     null_value = false;
     return str;
   }