diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 8418096c30..36de6d7e28 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 491bd29a1c..a42b8e9b53 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 2351024c22..e87ca90089 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 ed729dddc3..36826428a0 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 130a723f69..88a835e8aa 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
 --