--- hw/xfree86/modes/xf86EdidModes.c.orig	2007-09-29 17:01:58.097559000 +0200
+++ hw/xfree86/modes/xf86EdidModes.c	2007-09-29 17:03:07.269882000 +0200
@@ -401,8 +401,10 @@ xf86DDCMonitorSet(int scrnIndex, MonPtr 
 
     Monitor->DDC = DDC;
 
-    Monitor->widthmm = 10 * DDC->features.hsize;
-    Monitor->heightmm = 10 * DDC->features.vsize;
+    if (!Monitor->widthmm)
+	Monitor->widthmm = 10 * DDC->features.hsize;
+    if (!Monitor->heightmm)
+	Monitor->heightmm = 10 * DDC->features.vsize;
 
     /* If this is a digital display, then we can use reduced blanking */
     if (DDC->features.input_type)