diff --git a/src/tun.c b/src/tun.c
index 05c0a1e..61b3d12 100644
--- a/src/tun.c
+++ b/src/tun.c
@@ -93,11 +93,18 @@ tun_create_by_name(char *name, size_t len, const char *dev_name)
 static int
 tun_create_by_name(char *name, size_t len, const char *dev_name)
 {
+    int ret = snprintf(name, len, "%s", dev_name);
+
+    if (ret <= 0 || (size_t)ret >= len) {
+        errno = EINVAL;
+        return -1;
+    }
+
     struct ifreq ifr = {
         .ifr_flags = IFF_TUN | IFF_NO_PI,
     };
 
-    int ret = snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s", dev_name);
+    ret = snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s", dev_name);
 
     if (ret <= 0 || (size_t)ret >= sizeof(ifr.ifr_name)) {
         errno = EINVAL;