diff --git a/hw/xfree86/modes/xf86Crtc.c b/hw/xfree86/modes/xf86Crtc.c
index c4470c353..47d3ad14c 100644
--- a/hw/xfree86/modes/xf86Crtc.c
+++ b/hw/xfree86/modes/xf86Crtc.c
@@ -3016,6 +3016,8 @@ xf86OutputSetEDID (xf86OutputPtr output, xf86MonPtr edid_mon)
     free(output->MonInfo);
     
     output->MonInfo = edid_mon;
+    output->mm_width = 0;
+    output->mm_height = 0;
 
     if (debug_modes) {
 	xf86DrvMsg(scrn->scrnIndex, X_INFO, "EDID for output %s\n",