diff --git a/src/sock.c b/src/sock.c
index e32d152..27797a2 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -791,6 +791,10 @@ int patty_ax25_sock_ack(patty_ax25_sock *sock, int nr) {
         max = nr,
         i;
 
+    if (min == max) {
+        return 1;
+    }
+
     if (max < min) {
         max += sock->mode == PATTY_AX25_SOCK_SABME? 128: 8;
     }