diff --git a/drivers/video/atafb.c b/drivers/video/atafb.c
index 37624f7..b7687c5 100644
--- a/drivers/video/atafb.c
+++ b/drivers/video/atafb.c
@@ -2242,6 +2242,9 @@
 	if (!external_vgaiobase)
 		return 1;
 
+	if (regno > 255)
+		return 1;
+
 	switch (external_card_type) {
 	case IS_VGA:
 		OUTB(0x3c8, regno);