diff --git a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c
index 10e5d985afa..edfa15d2e79 100644
--- a/drivers/net/ppp_generic.c
+++ b/drivers/net/ppp_generic.c
@@ -1465,7 +1465,12 @@ static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb)
 			continue;
 		}
 
-		mtu = pch->chan->mtu - hdrlen;
+		/*
+		 * hdrlen includes the 2-byte PPP protocol field, but the
+		 * MTU counts only the payload excluding the protocol field.
+		 * (RFC1661 Section 2)
+		 */
+		mtu = pch->chan->mtu - (hdrlen - 2);
 		if (mtu < 4)
 			mtu = 4;
 		if (flen > mtu)