diff --git a/src/sock.c b/src/sock.c
index 830b7db..47ba896 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -101,6 +101,7 @@ static int init_bufs(patty_ax25_sock *sock) {
         struct slot *slot = tx_slot(sock, i);
 
         slot->len = 0;
+        slot->ack = 0;
     }
 
     return 0;