diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
index 797fab33bb983913d50864ce7c6a792a6c3a6f95..7cbea796652aca1ef537d9cdc68b645d340f73ee 100644
--- a/drivers/ptp/ptp_chardev.c
+++ b/drivers/ptp/ptp_chardev.c
@@ -224,7 +224,8 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 			extoff = NULL;
 			break;
 		}
-		if (extoff->n_samples > PTP_MAX_SAMPLES) {
+		if (extoff->n_samples > PTP_MAX_SAMPLES
+		    || extoff->rsv[0] || extoff->rsv[1] || extoff->rsv[2]) {
 			err = -EINVAL;
 			break;
 		}