diff --git a/src/sock.c b/src/sock.c
index ca983ca..c39df4a 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -89,8 +89,8 @@ static inline void tx_slot_save(patty_ax25_sock *sock, void *buf, size_t len) {
 }
 
 static int init_bufs(patty_ax25_sock *sock) {
-    size_t i,
-           slots = sock->mode == PATTY_AX25_SOCK_SABME? 128: 8;
+    size_t slots = tx_slots(sock),
+           i;
 
     if ((sock->tx_buf = realloc(sock->tx_buf, tx_bufsz(sock))) == NULL) {
         goto error_realloc_tx_buf;
@@ -815,9 +815,10 @@ int patty_ax25_sock_ack(patty_ax25_sock *sock, int nr) {
 }
 
 int patty_ax25_sock_ack_pending(patty_ax25_sock *sock) {
-    int ret   = 0,
-        slots = sock->mode == PATTY_AX25_SOCK_SABME? 128: 8,
-        i;
+    int ret = 0;
+
+    size_t slots = tx_slots(sock),
+           i;
 
     for (i=0; i<slots; i++) {
         struct slot *slot = tx_slot(sock, i);