diff --git a/TAP.c b/TAP.c
index 24b7cd4..8525060 100644
--- a/TAP.c
+++ b/TAP.c
@@ -100,14 +100,6 @@ void trySixSet
         interfaceIndex
     );
 
-    // linux IPv6 mtu check
-    if(mtu < 1280)
-    {
-        printf("MTU must be 1280 bytes or more for IPv6\n");
-        cleanup();
-        exit(1);
-    }
-
 	int dummySock = socket(AF_INET6, SOCK_DGRAM, 0);
 
 	struct in6_ifreq paramReq;
@@ -318,6 +310,14 @@ int open_tap(void) {
 
                                 if(set_ipv6 || link_local_v6)
                                 {
+                                    // linux IPv6 mtu check
+                                    if(mtu < 1280)
+                                    {
+                                        printf("MTU must be 1280 bytes or more for IPv6\n");
+                                        cleanup();
+                                        exit(1);
+                                    }
+                                    
                                     // Firstly, obtain the interface index by `ifr_name`
                                     int dummySock = socket(AF_INET6, SOCK_DGRAM, 0);
                                     if(ioctl(dummySock, SIOCGIFINDEX, &ifr) < 0)