diff --git a/sys/netinet/ip_input.c b/sys/netinet/ip_input.c
index 8be51fb992da..fdef6457b3e5 100644
--- a/sys/netinet/ip_input.c
+++ b/sys/netinet/ip_input.c
@@ -1590,7 +1590,7 @@ ip_forward(struct mbuf *m, int srcrt)
 		 * If IPsec is configured for this path,
 		 * override any possibly mtu value set by ip_output.
 		 */ 
-		mtu = ip_ipsec_mtu(m, mtu);
+		mtu = ip_ipsec_mtu(mcopy, mtu);
 #endif /* IPSEC */
 		/*
 		 * If the MTU was set before make sure we are below the