diff --git a/src/bin/pg_upgrade/t/003_logical_slots.pl b/src/bin/pg_upgrade/t/003_logical_slots.pl
index c628d51dfe6..01ab82402ae 100644
--- a/src/bin/pg_upgrade/t/003_logical_slots.pl
+++ b/src/bin/pg_upgrade/t/003_logical_slots.pl
@@ -66,19 +66,6 @@ $oldpub->safe_psql(
 	SELECT pg_create_logical_replication_slot('test_slot2', 'test_decoding');
 	SELECT pg_create_logical_replication_slot('test_slot3', 'test_decoding');
 ]);
-
-# check.c assumes the list syntax of output_plugin_libraries is validated by the
-# server, so take a moment to confirm that now. (This is difficult to test via
-# regression suite, because our SET grammar won't accept the bad syntax.)
-$oldpub->connect_fails(
-	"options='-c output_plugin_libraries=pgoutput,'",
-	"server validates output_plugin_libraries syntax",
-	expected_stderr => qr[
-		\Qinvalid value for parameter "output_plugin_libraries"\E
-		.*
-		\QList syntax is invalid.\E
-	]sx);
-
 $oldpub->stop();
 
 # 2. Set 'max_replication_slots' to be less than the number of slots (2)
diff --git a/src/test/regress/expected/guc.out b/src/test/regress/expected/guc.out
index 0c18fc94e31..a85ea63a935 100644
--- a/src/test/regress/expected/guc.out
+++ b/src/test/regress/expected/guc.out
@@ -53,6 +53,10 @@ LINE 1: SET search_path = null, null;
 SET enable_seqscan = null;  -- error
 ERROR:  NULL is an invalid value for enable_seqscan
 RESET search_path;
+-- Check syntax validation of output_plugin_libraries
+SELECT set_config('output_plugin_libraries', 'pgoutput,', false);
+ERROR:  invalid value for parameter "output_plugin_libraries": "pgoutput,"
+DETAIL:  List syntax is invalid.
 -- SET LOCAL has no effect outside of a transaction
 SET LOCAL vacuum_cost_delay TO 50;
 WARNING:  SET LOCAL can only be used in transaction blocks
diff --git a/src/test/regress/sql/guc.sql b/src/test/regress/sql/guc.sql
index e78b4af3a3a..31702df9d18 100644
--- a/src/test/regress/sql/guc.sql
+++ b/src/test/regress/sql/guc.sql
@@ -21,6 +21,9 @@ SET search_path = null, null;  -- syntax error
 SET enable_seqscan = null;  -- error
 RESET search_path;
 
+-- Check syntax validation of output_plugin_libraries
+SELECT set_config('output_plugin_libraries', 'pgoutput,', false);
+
 -- SET LOCAL has no effect outside of a transaction
 SET LOCAL vacuum_cost_delay TO 50;
 SHOW vacuum_cost_delay;