diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 8ca6bcab7b03..18c8baf32de5 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1013,13 +1013,14 @@ out:	kfree_skb(skb);
 static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
 {
 	struct dst_entry *dst = &rt->dst;
-	u32 old_mtu = ipv4_mtu(dst);
 	struct fib_result res;
 	bool lock = false;
+	u32 old_mtu;
 
 	if (ip_mtu_locked(dst))
 		return;
 
+	old_mtu = ipv4_mtu(dst);
 	if (old_mtu < mtu)
 		return;