diff --git a/test_mx_util.c b/test_mx_util.c
index 387db1f6..9ecf5343 100644
--- a/test_mx_util.c
+++ b/test_mx_util.c
@@ -576,6 +576,19 @@ static void test_mx_pipe_external(void) {
     }
 }
 
+static void test_mx_call_external(void) {
+    int sts;
+    errno = 999;
+
+    sts = mx_call_external("/usr/bin/true", NULL);
+    assert(sts == 0);
+    assert(errno == 999);
+
+    sts = mx_call_external("/usr/bin/false", NULL);
+    assert(sts == -1);
+    assert(errno == EPROTO);
+}
+
 int main(void)
 {
     test_mx_strskipwhitespaces();
@@ -597,5 +610,6 @@ int main(void)
     test_listsort();
     test_mx_df();
     test_mx_pipe_external();
+    test_mx_call_external();
     return 0;
 }