diff --git a/sql/field.h b/sql/field.h
index 8829aac65bd..936babdd26a 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -1000,20 +1000,23 @@ public:
 
 class Field_string :public Field_longstr {
 public:
+  bool can_alter_field_type;
   Field_string(char *ptr_arg, uint32 len_arg,uchar *null_ptr_arg,
 	       uchar null_bit_arg,
 	       enum utype unireg_check_arg, const char *field_name_arg,
 	       CHARSET_INFO *cs)
     :Field_longstr(ptr_arg, len_arg, null_ptr_arg, null_bit_arg,
-                   unireg_check_arg, field_name_arg, cs) {};
+                   unireg_check_arg, field_name_arg, cs),
+     can_alter_field_type(1) {};
   Field_string(uint32 len_arg,bool maybe_null_arg, const char *field_name_arg,
                CHARSET_INFO *cs)
     :Field_longstr((char*) 0, len_arg, maybe_null_arg ? (uchar*) "": 0, 0,
-                   NONE, field_name_arg, cs) {};
+                   NONE, field_name_arg, cs),
+     can_alter_field_type(1) {};
 
   enum_field_types type() const
   {
-    return ((orig_table &&
+    return ((can_alter_field_type && orig_table &&
              orig_table->s->db_create_options & HA_OPTION_PACK_RECORD &&
 	     field_length >= 4) &&
             orig_table->s->frm_version < FRM_VER_TRUE_VARCHAR ?
diff --git a/sql/sql_update.cc b/sql/sql_update.cc
index b19d6504b2e..75e8db6621f 100644
--- a/sql/sql_update.cc
+++ b/sql/sql_update.cc
@@ -1229,6 +1229,11 @@ multi_update::initialize_tables(JOIN *join)
     Field_string offset(table->file->ref_length, 0, "offset",
 			&my_charset_bin);
     offset.init(table);
+    /*
+      The field will be converted to varstring when creating tmp table if
+      table to be updated was created by mysql 4.1. Deny this.
+    */
+    offset.can_alter_field_type= 0;
     if (!(ifield= new Item_field(((Field *) &offset))))
       DBUG_RETURN(1);
     ifield->maybe_null= 0;