diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 5d84285752..299d8ccd81 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -6603,12 +6603,12 @@ static ObjectAddress
 ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
 					  bool recurse, bool recursing, LOCKMODE lockmode)
 {
+	Constraint *cmdcon;
 	Relation	conrel;
 	SysScanDesc scan;
 	ScanKeyData key;
 	HeapTuple	contuple;
 	Form_pg_constraint currcon = NULL;
-	Constraint *cmdcon = NULL;
 	bool		found = false;
 	ObjectAddress address;
 
@@ -6655,10 +6655,11 @@ ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
 		HeapTuple	copyTuple;
 		HeapTuple	tgtuple;
 		Form_pg_constraint copy_con;
-		Form_pg_trigger copy_tg;
+		List	   *otherrelids = NIL;
 		ScanKeyData tgkey;
 		SysScanDesc tgscan;
 		Relation	tgrel;
+		ListCell   *lc;
 
 		/*
 		 * Now update the catalog, while we have the door open.
@@ -6691,8 +6692,16 @@ ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
 
 		while (HeapTupleIsValid(tgtuple = systable_getnext(tgscan)))
 		{
+			Form_pg_trigger copy_tg;
+
 			copyTuple = heap_copytuple(tgtuple);
 			copy_tg = (Form_pg_trigger) GETSTRUCT(copyTuple);
+
+			/* Remember OIDs of other relation(s) involved in FK constraint */
+			if (copy_tg->tgrelid != RelationGetRelid(rel))
+				otherrelids = list_append_unique_oid(otherrelids,
+													 copy_tg->tgrelid);
+
 			copy_tg->tgdeferrable = cmdcon->deferrable;
 			copy_tg->tginitdeferred = cmdcon->initdeferred;
 			simple_heap_update(tgrel, &copyTuple->t_self, copyTuple);
@@ -6709,9 +6718,16 @@ ATExecAlterConstraint(Relation rel, AlterTableCmd *cmd,
 		heap_close(tgrel, RowExclusiveLock);
 
 		/*
-		 * Invalidate relcache so that others see the new attributes.
+		 * Invalidate relcache so that others see the new attributes.  We must
+		 * inval both the named rel and any others having relevant triggers.
+		 * (At present there should always be exactly one other rel, but
+		 * there's no need to hard-wire such an assumption here.)
 		 */
 		CacheInvalidateRelcache(rel);
+		foreach(lc, otherrelids)
+		{
+			CacheInvalidateRelcacheByRelid(lfirst_oid(lc));
+		}
 
 		ObjectAddressSet(address, ConstraintRelationId,
 						 HeapTupleGetOid(contuple));
diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out
index 0299bfe873..8c47babb6d 100644
--- a/src/test/regress/expected/foreign_key.out
+++ b/src/test/regress/expected/foreign_key.out
@@ -1132,15 +1132,6 @@ CREATE TEMP TABLE fktable (
     id int primary key,
     fk int references pktable deferrable initially deferred
 );
--- check ALTER CONSTRAINT
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE;
--- illegal option
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY DEFERRED;
-ERROR:  constraint declared INITIALLY DEFERRED must be DEFERRABLE
-LINE 1: ...e ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY ...
-                                                             ^
--- reset
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY DEFERRED;
 INSERT INTO pktable VALUES (5, 10);
 BEGIN;
 -- doesn't match PK, but no error yet
@@ -1151,16 +1142,6 @@ UPDATE fktable SET id = id + 1;
 COMMIT;
 ERROR:  insert or update on table "fktable" violates foreign key constraint "fktable_fk_fkey"
 DETAIL:  Key (fk)=(20) is not present in table "pktable".
--- change the constraint definition and retest
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY IMMEDIATE;
-BEGIN;
--- doesn't match PK, should throw error now
-INSERT INTO fktable VALUES (0, 20);
-ERROR:  insert or update on table "fktable" violates foreign key constraint "fktable_fk_fkey"
-DETAIL:  Key (fk)=(20) is not present in table "pktable".
-COMMIT;
--- reset
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY DEFERRED;
 -- check same case when insert is in a different subtransaction than update
 BEGIN;
 -- doesn't match PK, but no error yet
@@ -1198,6 +1179,30 @@ ROLLBACK TO savept1;
 COMMIT;
 ERROR:  insert or update on table "fktable" violates foreign key constraint "fktable_fk_fkey"
 DETAIL:  Key (fk)=(20) is not present in table "pktable".
+--
+-- check ALTER CONSTRAINT
+--
+INSERT INTO fktable VALUES (1, 5);
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY IMMEDIATE;
+BEGIN;
+-- doesn't match FK, should throw error now
+UPDATE pktable SET id = 10 WHERE id = 5;
+ERROR:  update or delete on table "pktable" violates foreign key constraint "fktable_fk_fkey" on table "fktable"
+DETAIL:  Key (id)=(5) is still referenced from table "fktable".
+COMMIT;
+BEGIN;
+-- doesn't match PK, should throw error now
+INSERT INTO fktable VALUES (0, 20);
+ERROR:  insert or update on table "fktable" violates foreign key constraint "fktable_fk_fkey"
+DETAIL:  Key (fk)=(20) is not present in table "pktable".
+COMMIT;
+-- try additional syntax
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE;
+-- illegal option
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY DEFERRED;
+ERROR:  constraint declared INITIALLY DEFERRED must be DEFERRABLE
+LINE 1: ...e ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY ...
+                                                             ^
 -- test order of firing of FK triggers when several RI-induced changes need to
 -- be made to the same row.  This was broken by subtransaction-related
 -- changes in 8.0.
diff --git a/src/test/regress/sql/foreign_key.sql b/src/test/regress/sql/foreign_key.sql
index 531c881f63..53276e4d67 100644
--- a/src/test/regress/sql/foreign_key.sql
+++ b/src/test/regress/sql/foreign_key.sql
@@ -818,13 +818,6 @@ CREATE TEMP TABLE fktable (
     fk int references pktable deferrable initially deferred
 );
 
--- check ALTER CONSTRAINT
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE;
--- illegal option
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY DEFERRED;
--- reset
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY DEFERRED;
-
 INSERT INTO pktable VALUES (5, 10);
 
 BEGIN;
@@ -838,19 +831,6 @@ UPDATE fktable SET id = id + 1;
 -- should catch error from initial INSERT
 COMMIT;
 
--- change the constraint definition and retest
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY IMMEDIATE;
-
-BEGIN;
-
--- doesn't match PK, should throw error now
-INSERT INTO fktable VALUES (0, 20);
-
-COMMIT;
-
--- reset
-ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY DEFERRED;
-
 -- check same case when insert is in a different subtransaction than update
 
 BEGIN;
@@ -900,6 +880,33 @@ ROLLBACK TO savept1;
 -- should catch error from initial INSERT
 COMMIT;
 
+--
+-- check ALTER CONSTRAINT
+--
+
+INSERT INTO fktable VALUES (1, 5);
+
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey DEFERRABLE INITIALLY IMMEDIATE;
+
+BEGIN;
+
+-- doesn't match FK, should throw error now
+UPDATE pktable SET id = 10 WHERE id = 5;
+
+COMMIT;
+
+BEGIN;
+
+-- doesn't match PK, should throw error now
+INSERT INTO fktable VALUES (0, 20);
+
+COMMIT;
+
+-- try additional syntax
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE;
+-- illegal option
+ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY DEFERRED;
+
 -- test order of firing of FK triggers when several RI-induced changes need to
 -- be made to the same row.  This was broken by subtransaction-related
 -- changes in 8.0.