diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index b043c60429bd45529111d56893dac55aae91427a..6b793bfc0e10b4fc42a5d7887e613d00e545ee70 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -811,11 +811,10 @@ static struct pernet_operations inet6_net_ops = {
 
 static int __init inet6_init(void)
 {
-	struct sk_buff *dummy_skb;
 	struct list_head *r;
 	int err = 0;
 
-	BUILD_BUG_ON(sizeof(struct inet6_skb_parm) > sizeof(dummy_skb->cb));
+	BUILD_BUG_ON(sizeof(struct inet6_skb_parm) > FIELD_SIZEOF(struct sk_buff, cb));
 
 	/* Register the socket-side information for inet6_create.  */
 	for (r = &inetsw6[0]; r < &inetsw6[SOCK_MAX]; ++r)