diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
index 2b0ae8cc8e51bc3ca52622f66e5909b537bd0153..da18c977e7b83f022db762779ec42d72cb2677b1 100644
--- a/drivers/input/mouse/alps.c
+++ b/drivers/input/mouse/alps.c
@@ -1156,7 +1156,13 @@ static psmouse_ret_t alps_process_byte(struct psmouse *psmouse)
 {
 	struct alps_data *priv = psmouse->private;
 
-	if ((psmouse->packet[0] & 0xc8) == 0x08) { /* PS/2 packet */
+	/*
+	 * Check if we are dealing with a bare PS/2 packet, presumably from
+	 * a device connected to the external PS/2 port. Because bare PS/2
+	 * protocol does not have enough constant bits to self-synchronize
+	 * properly we only do this if the device is fully synchronized.
+	 */
+	if (!psmouse->out_of_sync_cnt && (psmouse->packet[0] & 0xc8) == 0x08) {
 		if (psmouse->pktcnt == 3) {
 			alps_report_bare_ps2_packet(psmouse, psmouse->packet,
 						    true);