diff --git a/sys/dev/drm/radeon/rv740_dpm.c b/sys/dev/drm/radeon/rv740_dpm.c
--- a/sys/dev/drm/radeon/rv740_dpm.c
+++ b/sys/dev/drm/radeon/rv740_dpm.c
@@ -142,6 +142,7 @@
 	reference_divider = 1 + dividers.ref_div;
 
 	tmp = (u64) engine_clock * reference_divider * dividers.post_div * 16384;
+	if (reference_clock == 0) return -EINVAL;
 	do_div(tmp, reference_clock);
 	fbdiv = (u32) tmp;