diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index b96aa88087be1cc28179003f33b74b10a989088a..70e5e9e5d8351ee75eebd676ba40f9f8e2192eca 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -353,6 +353,8 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 		fl4.flowi4_proto = 0;
 		fl4.fl4_sport = 0;
 		fl4.fl4_dport = 0;
+	} else {
+		swap(fl4.fl4_sport, fl4.fl4_dport);
 	}
 
 	if (fib_lookup(net, &fl4, &res, 0))