diff --git a/api/modem/at/response.go b/api/modem/at/response.go
index aa1a4a3..d3d10f9 100644
--- a/api/modem/at/response.go
+++ b/api/modem/at/response.go
@@ -9,6 +9,9 @@ func (resp Resp) Check() bool {
 }
 
 func (resp Resp) RmFront(str string) Resp {
+	if !resp.Check() {
+		return RespNil
+	}
 	return Resp(string(resp)[len(str):])
 }