diff --git a/sys/dev/drm/radeon/atombios_dp.c b/sys/dev/drm/radeon/atombios_dp.c
--- a/sys/dev/drm/radeon/atombios_dp.c
+++ b/sys/dev/drm/radeon/atombios_dp.c
@@ -313,6 +313,9 @@
 	unsigned max_lane_num = drm_dp_max_lane_count(dpcd);
 	unsigned lane_num, i, max_pix_clock;
 
+	if (max_lane_num > 4)
+		max_lane_num = 4;
+
 	if (radeon_connector_encoder_get_dp_bridge_encoder_id(connector) ==
 	    ENCODER_OBJECT_ID_NUTMEG) {
 		for (lane_num = 1; lane_num <= max_lane_num; lane_num <<= 1) {