diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index c69c461b62..fb53d71cd6 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -28,6 +28,8 @@
 
 #include "nodes/makefuncs.h"
 
+#include "storage/lmgr.h"
+
 #include "utils/array.h"
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
@@ -246,6 +248,8 @@ SetSubscriptionRelState(Oid subid, Oid relid, char state,
 	bool		nulls[Natts_pg_subscription_rel];
 	Datum		values[Natts_pg_subscription_rel];
 
+	LockSharedObject(SubscriptionRelationId, subid, 0, AccessShareLock);
+
 	rel = heap_open(SubscriptionRelRelationId, RowExclusiveLock);
 
 	/* Try finding existing mapping. */
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 9cbd36f646..6dc3f6ee00 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -644,6 +644,9 @@ AlterSubscription(AlterSubscriptionStmt *stmt)
 	subid = HeapTupleGetOid(tup);
 	sub = GetSubscription(subid, false);
 
+	/* Lock the subscription so nobody else can do anything with it. */
+	LockSharedObject(SubscriptionRelationId, subid, 0, AccessExclusiveLock);
+
 	/* Form a new tuple. */
 	memset(values, 0, sizeof(values));
 	memset(nulls, false, sizeof(nulls));