diff --git a/mtu.c b/mtu.c
index 567d177..472bd4e 100644
--- a/mtu.c
+++ b/mtu.c
@@ -22,6 +22,7 @@
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 #include <sys/types.h>
+#include <unistd.h>
 
 #include "mtu.h"
 
@@ -33,14 +34,16 @@
   int fd;
   struct ifreq if_mtu;
 
-  fd = socket(AF_INET, SOCK_STREAM, 0);
+  fd = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
   if (fd < 0) {
     return -1;
   }
   strncpy(if_mtu.ifr_name, ifname, IFNAMSIZ);
   if_mtu.ifr_name[IFNAMSIZ - 1] = '\0';
   if (ioctl(fd, SIOCGIFMTU, &if_mtu) < 0) {
+    close(fd);
     return -1;
   }
+  close(fd);
   return if_mtu.ifr_mtu;
 }