diff --git a/devices/esp8266_tencent_firmware/esp8266_tencent_firmware.c b/devices/esp8266_tencent_firmware/esp8266_tencent_firmware.c
index 505648ccb223c2bdd9498f6bb451d8e22f13dac8..9974f9b567f09cab22e51ff30f908c31a63cc1b3 100644
--- a/devices/esp8266_tencent_firmware/esp8266_tencent_firmware.c
+++ b/devices/esp8266_tencent_firmware/esp8266_tencent_firmware.c
@@ -130,6 +130,10 @@ int esp8266_tencent_firmware_module_mqtt_state_get(mqtt_state_t *state)
     }
 
     str = strstr(echo.buffer, "+TCMQTTSTATE:");
+    if (!str) 
+    {
+        return -1;
+    }
     sscanf(str, "+TCMQTTSTATE:%d", &ret_state);
     if (ret_state == 0) {
         *state = MQTT_STATE_DISCONNECTED;