diff --git a/mbtk/mbtk_lib/src/mbtk_gnss_5311.c b/mbtk/mbtk_lib/src/mbtk_gnss_5311.c
index 8bbc64b..a3df60c 100755
--- a/mbtk/mbtk_lib/src/mbtk_gnss_5311.c
+++ b/mbtk/mbtk_lib/src/mbtk_gnss_5311.c
@@ -18,6 +18,7 @@
 #include <sys/ioctl.h>
 #include <termios.h>
 #include <sys/socket.h>
+#include <fcntl.h>
 
 #include <libubox/blobmsg_json.h>
 #include <libubus.h>
@@ -371,7 +372,7 @@
             if ((events[ne].events & (EPOLLERR|EPOLLHUP)) != 0)
             {
                 LOGE("[mbtk_gnss_api] EPOLLERR or EPOLLHUP after epoll_wait()!");
-                return;
+                return NULL;
             }
 
             if ((events[ne].events & EPOLLIN) != 0)