diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 8418096c308ab74e898afd9624a856099553ef38..36de6d7e28b1bf8c01e6d5edec5a0d62ed1fad68 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -1169,7 +1169,7 @@ DefineEnum(CreateEnumStmt *stmt)
* Adds a new label to an existing enum.
*/
void
-AlterEnum(AlterEnumStmt *stmt)
+AlterEnum(AlterEnumStmt *stmt, bool isTopLevel)
{
Oid enum_type_oid;
TypeName *typename;
@@ -1183,12 +1183,31 @@ AlterEnum(AlterEnumStmt *stmt)
if (!HeapTupleIsValid(tup))
elog(ERROR, "cache lookup failed for type %u", enum_type_oid);
+ /*
+ * Ordinarily we disallow adding values within transaction blocks, because
+ * we can't cope with enum OID values getting into indexes and then having
+ * their defining pg_enum entries go away. However, it's okay if the enum
+ * type was created in the current transaction, since then there can be
+ * no such indexes that wouldn't themselves go away on rollback. (We
+ * support this case because pg_dump --binary-upgrade needs it.) We test
+ * this by seeing if the pg_type row has xmin == current XID and is not
+ * HEAP_UPDATED. If it is HEAP_UPDATED, we can't be sure whether the
+ * type was created or only modified in this xact. So we are disallowing
+ * some cases that could theoretically be safe; but fortunately pg_dump
+ * only needs the simplest case.
+ */
+ if (HeapTupleHeaderGetXmin(tup->t_data) == GetCurrentTransactionId() &&
+ !(tup->t_data->t_infomask & HEAP_UPDATED))
+ /* safe to do inside transaction block */ ;
+ else
+ PreventTransactionChain(isTopLevel, "ALTER TYPE ... ADD");
+
/* Check it's an enum and check user has permission to ALTER the enum */
checkEnumOwner(tup);
/* Add the new label */
AddEnumLabel(enum_type_oid, stmt->newVal,
- stmt->newValNeighbor, stmt->newValIsAfter,
+ stmt->newValNeighbor, stmt->newValIsAfter,
stmt->skipIfExists);
ReleaseSysCache(tup);
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 491bd29a1c6f1f0ede999a7014da5422d75bc017..a42b8e9b535b8866678da484610eb242f2999a7f 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -972,14 +972,7 @@ standard_ProcessUtility(Node *parsetree,
case T_AlterEnumStmt: /* ALTER TYPE (enum) */
if (isCompleteQuery)
EventTriggerDDLCommandStart(parsetree);
-
- /*
- * We disallow this in transaction blocks, because we can't cope
- * with enum OID values getting into indexes and then having their
- * defining pg_enum entries go away.
- */
- PreventTransactionChain(isTopLevel, "ALTER TYPE ... ADD");
- AlterEnum((AlterEnumStmt *) parsetree);
+ AlterEnum((AlterEnumStmt *) parsetree, isTopLevel);
break;
case T_ViewStmt: /* CREATE VIEW */
diff --git a/src/include/commands/typecmds.h b/src/include/commands/typecmds.h
index 2351024c2212199dac3563c222aa171a3dacc8cd..e87ca900892555011e3f171cc985414c466bec83 100644
--- a/src/include/commands/typecmds.h
+++ b/src/include/commands/typecmds.h
@@ -26,7 +26,7 @@ extern void RemoveTypeById(Oid typeOid);
extern void DefineDomain(CreateDomainStmt *stmt);
extern void DefineEnum(CreateEnumStmt *stmt);
extern void DefineRange(CreateRangeStmt *stmt);
-extern void AlterEnum(AlterEnumStmt *stmt);
+extern void AlterEnum(AlterEnumStmt *stmt, bool isTopLevel);
extern Oid DefineCompositeType(RangeVar *typevar, List *coldeflist);
extern Oid AssignTypeArrayOid(void);
diff --git a/src/test/regress/expected/enum.out b/src/test/regress/expected/enum.out
index ed729dddc3f3fdfece86934d48c6645e480cef4a..36826428a07107b7289ce44ed608e4a15cbfcb93 100644
--- a/src/test/regress/expected/enum.out
+++ b/src/test/regress/expected/enum.out
@@ -556,6 +556,30 @@ ERROR: foreign key constraint "enumtest_bogus_child_parent_fkey" cannot be impl
DETAIL: Key columns "parent" and "id" are of incompatible types: bogus and rainbow.
DROP TYPE bogus;
--
+-- check transactional behaviour of ALTER TYPE ... ADD VALUE
+--
+CREATE TYPE bogus AS ENUM('good');
+-- check that we can't add new values to existing enums in a transaction
+BEGIN;
+ALTER TYPE bogus ADD VALUE 'bad';
+ERROR: ALTER TYPE ... ADD cannot run inside a transaction block
+COMMIT;
+-- check that we recognize the case where the enum already existed but was
+-- modified in the current txn
+BEGIN;
+ALTER TYPE bogus RENAME TO bogon;
+ALTER TYPE bogon ADD VALUE 'bad';
+ERROR: ALTER TYPE ... ADD cannot run inside a transaction block
+ROLLBACK;
+DROP TYPE bogus;
+-- check that we *can* add new values to existing enums in a transaction,
+-- if the type is new as well
+BEGIN;
+CREATE TYPE bogus AS ENUM();
+ALTER TYPE bogus ADD VALUE 'good';
+ALTER TYPE bogus ADD VALUE 'ugly';
+ROLLBACK;
+--
-- Cleanup
--
DROP TABLE enumtest_child;
diff --git a/src/test/regress/sql/enum.sql b/src/test/regress/sql/enum.sql
index 130a723f698afce670bb2b1abd12b050524457d2..88a835e8aaca0d64c3eb77ac562080f11613c515 100644
--- a/src/test/regress/sql/enum.sql
+++ b/src/test/regress/sql/enum.sql
@@ -257,6 +257,33 @@ CREATE TYPE bogus AS ENUM('good', 'bad', 'ugly');
CREATE TABLE enumtest_bogus_child(parent bogus REFERENCES enumtest_parent);
DROP TYPE bogus;
+--
+-- check transactional behaviour of ALTER TYPE ... ADD VALUE
+--
+CREATE TYPE bogus AS ENUM('good');
+
+-- check that we can't add new values to existing enums in a transaction
+BEGIN;
+ALTER TYPE bogus ADD VALUE 'bad';
+COMMIT;
+
+-- check that we recognize the case where the enum already existed but was
+-- modified in the current txn
+BEGIN;
+ALTER TYPE bogus RENAME TO bogon;
+ALTER TYPE bogon ADD VALUE 'bad';
+ROLLBACK;
+
+DROP TYPE bogus;
+
+-- check that we *can* add new values to existing enums in a transaction,
+-- if the type is new as well
+BEGIN;
+CREATE TYPE bogus AS ENUM();
+ALTER TYPE bogus ADD VALUE 'good';
+ALTER TYPE bogus ADD VALUE 'ugly';
+ROLLBACK;
+
--
-- Cleanup
--