diff --git a/hw/xfree86/common/xf86RandR.c b/hw/xfree86/common/xf86RandR.c
index f30674f72..10ec37070 100644
--- a/hw/xfree86/common/xf86RandR.c
+++ b/hw/xfree86/common/xf86RandR.c
@@ -55,6 +55,8 @@ xf86RandRModeRefresh (DisplayModePtr mode)
 {
     if (mode->VRefresh)
 	return (int) (mode->VRefresh + 0.5);
+    else if (mode->Clock == 0)
+	return 0;
     else
 	return (int) (mode->Clock * 1000.0 / mode->HTotal / mode->VTotal + 0.5);
 }