diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 625a38ccb5d9..820eae3ea95f 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -316,12 +316,13 @@ static inline bool rt6_duplicate_nexthop(struct fib6_info *a, struct fib6_info *
 	       !lwtunnel_cmp_encap(nha->fib_nh_lws, nhb->fib_nh_lws);
 }
 
-static inline unsigned int ip6_dst_mtu_forward(const struct dst_entry *dst)
+static inline unsigned int ip6_dst_mtu_maybe_forward(const struct dst_entry *dst,
+						     bool forwarding)
 {
 	struct inet6_dev *idev;
 	unsigned int mtu;
 
-	if (dst_metric_locked(dst, RTAX_MTU)) {
+	if (!forwarding || dst_metric_locked(dst, RTAX_MTU)) {
 		mtu = dst_metric_raw(dst, RTAX_MTU);
 		if (mtu)
 			goto out;
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 01bea76e3891..f6bc7828a480 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -607,7 +607,7 @@ int ip6_forward(struct sk_buff *skb)
 		}
 	}
 
-	mtu = ip6_dst_mtu_forward(dst);
+	mtu = ip6_dst_mtu_maybe_forward(dst, true);
 	if (mtu < IPV6_MIN_MTU)
 		mtu = IPV6_MIN_MTU;
 
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 5f7286acca33..21d5d0b4cde5 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3201,25 +3201,7 @@ static unsigned int ip6_default_advmss(const struct dst_entry *dst)
 
 INDIRECT_CALLABLE_SCOPE unsigned int ip6_mtu(const struct dst_entry *dst)
 {
-	struct inet6_dev *idev;
-	unsigned int mtu;
-
-	mtu = dst_metric_raw(dst, RTAX_MTU);
-	if (mtu)
-		goto out;
-
-	mtu = IPV6_MIN_MTU;
-
-	rcu_read_lock();
-	idev = __in6_dev_get(dst->dev);
-	if (idev)
-		mtu = idev->cnf.mtu6;
-	rcu_read_unlock();
-
-out:
-	mtu = min_t(unsigned int, mtu, IP6_MAX_MTU);
-
-	return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
+	return ip6_dst_mtu_maybe_forward(dst, false);
 }
 EXPORT_INDIRECT_CALLABLE(ip6_mtu);
 
diff --git a/net/netfilter/nf_flow_table_core.c b/net/netfilter/nf_flow_table_core.c
index 1e50908b1b7e..8fe024a0ae46 100644
--- a/net/netfilter/nf_flow_table_core.c
+++ b/net/netfilter/nf_flow_table_core.c
@@ -99,7 +99,7 @@ static int flow_offload_fill_route(struct flow_offload *flow,
 		flow_tuple->mtu = ip_dst_mtu_maybe_forward(dst, true);
 		break;
 	case NFPROTO_IPV6:
-		flow_tuple->mtu = ip6_dst_mtu_forward(dst);
+		flow_tuple->mtu = ip6_dst_mtu_maybe_forward(dst, true);
 		break;
 	}