diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index 5a48df0fc5e..46f188d4731 100644
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -4300,7 +4300,15 @@ RemoveTempRelationsCallback(int code, Datum arg)
 		/* Need to ensure we have a usable transaction. */
 		AbortOutOfAnyTransaction();
 		StartTransactionCommand();
-		PushActiveSnapshot(GetTransactionSnapshot());
+
+		/*
+		 * Need an active snapshot for toast fetches during deletion.  Do not
+		 * use GetTransactionSnapshot(): under SERIALIZABLE READ ONLY
+		 * DEFERRABLE it may wait in GetSafeSnapshot(), and proc_exit holds
+		 * off interrupts so that wait cannot be cancelled.  A catalog
+		 * snapshot is enough and avoids that path.
+		 */
+		PushActiveSnapshot(GetCatalogSnapshot(RelationRelationId));
 
 		RemoveTempRelations(myTempNamespace);
 
diff --git a/src/test/modules/test_misc/t/015_temp_schema_exit_deferrable.pl b/src/test/modules/test_misc/t/015_temp_schema_exit_deferrable.pl
new file mode 100644
index 00000000000..07de36630a6
--- /dev/null
+++ b/src/test/modules/test_misc/t/015_temp_schema_exit_deferrable.pl
@@ -0,0 +1,58 @@
+# Copyright (c) 2026, PostgreSQL Global Development Group
+
+# Backend exit must finish temp-schema cleanup even when the session default
+# is SERIALIZABLE READ ONLY DEFERRABLE and a prepared serializable transaction
+# is still around.
+
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('deferrable_temp_exit');
+$node->init;
+$node->append_conf('postgresql.conf', 'max_prepared_transactions = 1');
+$node->start;
+
+my $psql1 = $node->background_psql('postgres');
+
+$psql1->query_safe(
+	q{
+CREATE TEMPORARY TABLE tt (i int);
+SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL SERIALIZABLE READ ONLY DEFERRABLE;
+});
+
+my $pid = $psql1->query_safe(q{SELECT pg_backend_pid();});
+chomp $pid;
+like($pid, qr/^\d+$/, "backend pid $pid");
+
+# Overlapping read/write serializable xact that outlives session 1.
+$node->safe_psql(
+	'postgres',
+	q{
+CREATE TABLE t (i int);
+BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+INSERT INTO t VALUES (1);
+PREPARE TRANSACTION 'pt';
+});
+
+# Disconnect: RemoveTempRelationsCallback runs during backend exit.
+$psql1->quit;
+
+ok( $node->poll_query_until(
+		'postgres',
+		"SELECT count(*) = 0 FROM pg_stat_activity WHERE pid = $pid"),
+	'backend exited despite prepared serializable xact');
+
+is( $node->safe_psql(
+		'postgres',
+		q{SELECT count(*) FROM pg_class WHERE relname = 'tt' AND relpersistence = 't'}
+	),
+	'0',
+	'temporary table cleaned up on exit');
+
+$node->safe_psql('postgres', q{ROLLBACK PREPARED 'pt';});
+$node->safe_psql('postgres', q{DROP TABLE t;});
+
+done_testing();