diff --git a/test_mx_util.c b/test_mx_util.c
index 4c447d7..7baa716 100644
--- a/test_mx_util.c
+++ b/test_mx_util.c
@@ -597,11 +597,13 @@ static void test_mx_call_external(void) {
     int sts;
     errno = 999;
 
-    sts = mx_call_external("/usr/bin/true", NULL);
+    char *argv[] = { "", NULL };
+
+    sts = mx_call_external("/usr/bin/true", argv);
     assert(sts == 0);
     assert(errno == 999);
 
-    sts = mx_call_external("/usr/bin/false", NULL);
+    sts = mx_call_external("/usr/bin/false", argv);
     assert(sts == -1);
     assert(errno == EPROTO);
 }