diff --git a/mysql-test/r/type_enum.result b/mysql-test/r/type_enum.result
index 2a08a140087..02d71c6bd9f 100644
--- a/mysql-test/r/type_enum.result
+++ b/mysql-test/r/type_enum.result
@@ -2225,6 +2225,9 @@ a
 
 DROP TABLE t1;
 #
+# Start of 10.3 tests
+#
+#
 # MDEV-12432 Range optimizer for ENUM and SET does not return "Impossible WHERE" in some case
 #
 CREATE TABLE t1 (a ENUM('a','b','c','1'),KEY(a));
@@ -2257,3 +2260,54 @@ EXPLAIN SELECT * FROM t1 WHERE a='1.1';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 DROP TABLE t1;
+#
+# MDEV-12656 Crash in CREATE..SELECT..UNION with a ENUM column and NULL
+#
+CREATE TABLE t1 (a ENUM('a'));
+# non-UNION + table column
+CREATE TABLE t2 AS SELECT (SELECT a FROM t1);
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `(SELECT a FROM t1)` varchar(1) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t2;
+# UNION + table column
+CREATE TABLE t2 AS SELECT (SELECT a FROM t1 UNION SELECT NULL);
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `(SELECT a FROM t1 UNION SELECT NULL)` varchar(1) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t2;
+# UNION + SP variable
+CREATE PROCEDURE p1()
+BEGIN
+DECLARE va ENUM('a');
+CREATE TABLE t2 AS SELECT (SELECT va FROM t1 UNION SELECT NULL);
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+END;
+$$
+CALL p1();
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `(SELECT va FROM t1 UNION SELECT NULL)` varchar(1) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP PROCEDURE p1;
+# UNION + anchored SP variable
+CREATE PROCEDURE p1()
+BEGIN
+DECLARE va TYPE OF t1.a;
+CREATE TABLE t2 AS SELECT (SELECT va FROM t1 UNION SELECT NULL);
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+END;
+$$
+CALL p1();
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `(SELECT va FROM t1 UNION SELECT NULL)` varchar(1) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP PROCEDURE p1;
+DROP TABLE t1;
diff --git a/mysql-test/t/type_enum.test b/mysql-test/t/type_enum.test
index d00cf66ccb0..a79335960bc 100644
--- a/mysql-test/t/type_enum.test
+++ b/mysql-test/t/type_enum.test
@@ -457,6 +457,10 @@ ALTER TABLE t1 MODIFY a ENUM('2001','2002');
 SELECT * FROM t1;
 DROP TABLE t1;
 
+--echo #
+--echo # Start of 10.3 tests
+--echo #
+
 --echo #
 --echo # MDEV-12432 Range optimizer for ENUM and SET does not return "Impossible WHERE" in some case
 --echo #
@@ -473,3 +477,44 @@ EXPLAIN SELECT * FROM t1 WHERE a='1x';
 EXPLAIN SELECT * FROM t1 WHERE a='1.0';
 EXPLAIN SELECT * FROM t1 WHERE a='1.1';
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-12656 Crash in CREATE..SELECT..UNION with a ENUM column and NULL
+--echo #
+
+CREATE TABLE t1 (a ENUM('a'));
+--echo # non-UNION + table column
+CREATE TABLE t2 AS SELECT (SELECT a FROM t1);
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+--echo # UNION + table column
+CREATE TABLE t2 AS SELECT (SELECT a FROM t1 UNION SELECT NULL);
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+--echo # UNION + SP variable
+DELIMITER $$;
+CREATE PROCEDURE p1()
+BEGIN
+  DECLARE va ENUM('a');
+  CREATE TABLE t2 AS SELECT (SELECT va FROM t1 UNION SELECT NULL);
+  SHOW CREATE TABLE t2;
+  DROP TABLE t2;
+END;
+$$
+DELIMITER ;$$
+CALL p1();
+DROP PROCEDURE p1;
+--echo # UNION + anchored SP variable
+DELIMITER $$;
+CREATE PROCEDURE p1()
+BEGIN
+  DECLARE va TYPE OF t1.a;
+  CREATE TABLE t2 AS SELECT (SELECT va FROM t1 UNION SELECT NULL);
+  SHOW CREATE TABLE t2;
+  DROP TABLE t2;
+END;
+$$
+DELIMITER ;$$
+CALL p1();
+DROP PROCEDURE p1;
+DROP TABLE t1;
diff --git a/sql/item.cc b/sql/item.cc
index c0c99dc22bb..416f889712a 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -10072,7 +10072,7 @@ bool Item_type_holder::join_types(THD *thd, Item *item)
   if (aggregate_for_result(item_type_handler))
   {
     my_error(ER_ILLEGAL_PARAMETER_DATA_TYPES2_FOR_OPERATION, MYF(0),
-             Item_type_holder::type_handler()->name().ptr(),
+             Item_type_holder::real_type_handler()->name().ptr(),
              item_type_handler->name().ptr(),
              "UNION");
     DBUG_RETURN(true);
@@ -10180,7 +10180,14 @@ bool Item_type_holder::join_types(THD *thd, Item *item)
   };
   maybe_null|= item->maybe_null;
   get_full_info(item);
-  set_handler(Item_type_holder::type_handler()->type_handler_for_union(this));
+  /*
+    Adjust data type for union, e.g.:
+    - convert type_handler_null to type_handler_string
+    - convert type_handler_olddecimal to type_handler_newdecimal
+    - adjust varchar/blob according to max_length
+  */
+  set_handler(Item_type_holder::
+                real_type_handler()->type_handler_for_union(this));
 
   /* Remember decimal integer part to be used in DECIMAL_RESULT handleng */
   prev_decimal_int_part= decimal_int_part();
diff --git a/sql/item.h b/sql/item.h
index 1123b4beb93..0e004571395 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -2604,11 +2604,7 @@ public:
   const Type_handler *type_handler() const
   {
     const Type_handler *handler= field->type_handler();
-    // This special code for ENUM and SET should eventually be removed
-    if (handler == &type_handler_enum ||
-        handler == &type_handler_set)
-      return &type_handler_string;
-    return field->type_handler();
+    return handler->type_handler_for_item_field();
   }
   enum Item_result result_type () const
   {
@@ -5792,7 +5788,10 @@ public:
   Item_type_holder(THD*, Item*);
 
   const Type_handler *type_handler() const
-  { return Type_handler_hybrid_field_type::type_handler(); }
+  {
+    const Type_handler *handler= Type_handler_hybrid_field_type::type_handler();
+    return handler->type_handler_for_item_field();
+  }
   enum_field_types field_type() const
   { return Type_handler_hybrid_field_type::field_type(); }
   enum Item_result result_type () const
@@ -5813,7 +5812,7 @@ public:
   }
   const Type_handler *real_type_handler() const
   {
-    return Item_type_holder::type_handler();
+    return Type_handler_hybrid_field_type::type_handler();
   }
 
   enum Type type() const { return TYPE_HOLDER; }
@@ -5825,7 +5824,7 @@ public:
   bool join_types(THD *thd, Item *);
   Field *create_tmp_field(bool group, TABLE *table)
   {
-    return Item_type_holder::type_handler()->
+    return Item_type_holder::real_type_handler()->
            make_and_init_table_field(&name, Record_addr(maybe_null),
                                      *this, table);
   }
diff --git a/sql/sql_type.cc b/sql/sql_type.cc
index 88ad5bd576c..23cfe20e5e6 100644
--- a/sql/sql_type.cc
+++ b/sql/sql_type.cc
@@ -470,12 +470,24 @@ const Type_handler *Type_handler_row::type_handler_for_comparison() const
 
 /***************************************************************************/
 
+const Type_handler *Type_handler_enum::type_handler_for_item_field() const
+{
+  return &type_handler_string;
+}
+
+
 const Type_handler *Type_handler_enum::cast_to_int_type_handler() const
 {
   return &type_handler_longlong;
 }
 
 
+const Type_handler *Type_handler_set::type_handler_for_item_field() const
+{
+  return &type_handler_string;
+}
+
+
 const Type_handler *Type_handler_set::cast_to_int_type_handler() const
 {
   return &type_handler_longlong;
diff --git a/sql/sql_type.h b/sql/sql_type.h
index a1a2beeb1d1..c61142d0a7b 100644
--- a/sql/sql_type.h
+++ b/sql/sql_type.h
@@ -579,6 +579,10 @@ public:
   */
   virtual bool is_param_long_data_type() const { return false; }
   virtual const Type_handler *type_handler_for_comparison() const= 0;
+  virtual const Type_handler *type_handler_for_item_field() const
+  {
+    return this;
+  }
   virtual const Type_handler *type_handler_for_tmp_table(const Item *) const
   {
     return this;
@@ -2053,6 +2057,7 @@ public:
   const Name name() const { return m_name_enum; }
   enum_field_types field_type() const { return MYSQL_TYPE_STRING; }
   virtual enum_field_types real_field_type() const { return MYSQL_TYPE_ENUM; }
+  const Type_handler *type_handler_for_item_field() const;
   const Type_handler *cast_to_int_type_handler() const;
   Field *make_conversion_table_field(TABLE *, uint metadata,
                                      const Field *target) const;
@@ -2071,6 +2076,7 @@ public:
   const Name name() const { return m_name_set; }
   enum_field_types field_type() const { return MYSQL_TYPE_STRING; }
   virtual enum_field_types real_field_type() const { return MYSQL_TYPE_SET; }
+  const Type_handler *type_handler_for_item_field() const;
   const Type_handler *cast_to_int_type_handler() const;
   Field *make_conversion_table_field(TABLE *, uint metadata,
                                      const Field *target) const;