diff --git a/tests/server/mqttd.c b/tests/server/mqttd.c
index 744517077c..4fdc67c8af 100644
--- a/tests/server/mqttd.c
+++ b/tests/server/mqttd.c
@@ -583,6 +583,12 @@ static curl_socket_t mqttit(curl_socket_t fd)
 
       logmsg("SUBSCRIBE to '%s' [%d]", topic, packet_id);
       stream = test2fopen(testno, logdir);
+      if(!stream) {
+        error = errno;
+        logmsg("fopen() failed with error (%d) %s", error, strerror(error));
+        logmsg("Couldn't open test file %ld", testno);
+        goto end;
+      }
       error = getpart(&data, &datalen, "reply", "data", stream);
       if(!error) {
         if(!m_config.publish_before_suback) {