diff --git a/packet.c b/packet.c
index ab4d70afaac45e0cd397afcb71baada5b28e71e3..6c90a766ac9dd55060a542a1016c3fa47f667ff1 100644
--- a/packet.c
+++ b/packet.c
@@ -531,7 +531,7 @@ static void writemac(buffer * outputbuffer, buffer * clearwritebuf) {
 
 	TRACE(("enter writemac"))
 
-	macsize = ses.keys->recv_algo_mac->hashsize;
+	macsize = ses.keys->trans_algo_mac->hashsize;
 	if (macsize > 0) {
 		/* calculate the mac */
 		if (hmac_init(&hmac,