diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index cb4a0f4..82c11dd 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -951,7 +951,7 @@
 			addend += 4;
 	}
 	dev->needed_headroom = addend + hlen;
-	mtu -= dev->hard_header_len - addend;
+	mtu -= dev->hard_header_len + addend;
 
 	if (mtu < 68)
 		mtu = 68;