diff --git a/src/test/isolation/isolation_main.c b/src/test/isolation/isolation_main.c
index 31a0e6b709..a88e9da255 100644
--- a/src/test/isolation/isolation_main.c
+++ b/src/test/isolation/isolation_main.c
@@ -89,7 +89,7 @@ isolation_start_test(const char *testname,
 	offset += snprintf(psql_cmd + offset, sizeof(psql_cmd) - offset,
 					   "\"%s\" \"dbname=%s\" < \"%s\" > \"%s\" 2>&1",
 					   isolation_exec,
-					   dblist->str,
+					   dblist ? dblist->str : "",
 					   infile,
 					   outfile);
 	if (offset >= sizeof(psql_cmd))
diff --git a/src/test/regress/pg_regress_main.c b/src/test/regress/pg_regress_main.c
index a4b354c9e6..4e089b0f83 100644
--- a/src/test/regress/pg_regress_main.c
+++ b/src/test/regress/pg_regress_main.c
@@ -81,7 +81,7 @@ psql_start_test(const char *testname,
 					   "\"%s%spsql\" -X -a -q -d \"%s\" %s < \"%s\" > \"%s\" 2>&1",
 					   bindir ? bindir : "",
 					   bindir ? "/" : "",
-					   dblist->str,
+					   dblist ? dblist->str : "",
 					   "-v HIDE_TABLEAM=on -v HIDE_TOAST_COMPRESSION=on",
 					   infile,
 					   outfile);