diff --git a/drivers/media/dvb-frontends/si21xx.c b/drivers/media/dvb-frontends/si21xx.c
index 73b47cc6a13b3b8c2f6ca85d0ee1d9eee71120c1..16850e2bf02fe37bccc4c54af466a43f5dd61b85 100644
--- a/drivers/media/dvb-frontends/si21xx.c
+++ b/drivers/media/dvb-frontends/si21xx.c
@@ -236,6 +236,9 @@ static int si21_writeregs(struct si21xx_state *state, u8 reg1,
 				.len = len + 1
 	};
 
+	if (len > sizeof(buf) - 1)
+		return -EINVAL;
+
 	msg.buf[0] =  reg1;
 	memcpy(msg.buf + 1, data, len);