diff --git a/contrib/test_shm_mq/setup.c b/contrib/test_shm_mq/setup.c
index e50f1f0013..3e762c49a6 100644
--- a/contrib/test_shm_mq/setup.c
+++ b/contrib/test_shm_mq/setup.c
@@ -102,7 +102,7 @@ setup_dynamic_shared_memory(int64 queue_size, int nworkers,
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("queue size must be at least %lu bytes",
-					shm_mq_minimum_size)));
+					(unsigned long) shm_mq_minimum_size)));
 
 	/*
 	 * Estimate how much shared memory we need.