diff --git a/contrib/pg_upgrade/server.c b/contrib/pg_upgrade/server.c
index db62249637..5fdaba658b 100644
--- a/contrib/pg_upgrade/server.c
+++ b/contrib/pg_upgrade/server.c
@@ -215,7 +215,7 @@ start_postmaster(ClusterInfo *cluster)
 	 * win on ext4.
 	 */
 	snprintf(cmd, sizeof(cmd),
-			 "\"%s/pg_ctl\" -w -l \"%s\" -D \"%s\" -o \"-p %d%s%s%s%s\" start",
+			 "\"%s/pg_ctl\" -w -l \"%s\" -D \"%s\" -o \"-p %d%s%s %s%s\" start",
 		  cluster->bindir, SERVER_LOG_FILE, cluster->pgconfig, cluster->port,
 			 (cluster->controldata.cat_ver >=
 			  BINARY_UPGRADE_SERVER_FLAG_CAT_VER) ? " -b" :