diff --git a/src/sock.c b/src/sock.c
index 65024b9..dc6f3a6 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -390,8 +390,8 @@ ssize_t patty_ax25_sock_send(patty_ax25_sock *sock,
      size_t offset = 0;
     ssize_t encoded;
 
-    uint8_t *buf = PATTY_AX25_FRAME_CONTROL_U(control)?
-        sock->tx_buf: tx_slot(sock, sock->seq_send);
+    uint8_t *buf = PATTY_AX25_FRAME_CONTROL_I(control)?
+        tx_slot(sock, sock->seq_send): sock->tx_buf;
 
     if (sock->iface == NULL) {
         errno = ENETDOWN;