diff --git a/sys/dev/drm/radeon/rs780_dpm.c b/sys/dev/drm/radeon/rs780_dpm.c
--- a/sys/dev/drm/radeon/rs780_dpm.c
+++ b/sys/dev/drm/radeon/rs780_dpm.c
@@ -363,6 +363,9 @@
 {
 	struct igp_power_info *pi = rs780_get_pi(rdev);
 
+	if (pi->refresh_rate == 0)
+		return;
+
 	WREG32(FVTHROT_TARGET_REG, 30000000 / pi->refresh_rate);
 	WREG32(FVTHROT_CB1, 1000000 * 5 / pi->refresh_rate);
 	WREG32(FVTHROT_CB2, 1000000 * 10 / pi->refresh_rate);