diff --git a/src/VBox/Additions/x11/vboxvideo/vboxvideo.c b/src/VBox/Additions/x11/vboxvideo/vboxvideo.c
index 17f37e7..e782286 100644
--- a/src/VBox/Additions/x11/vboxvideo/vboxvideo.c
+++ b/src/VBox/Additions/x11/vboxvideo/vboxvideo.c
@@ -1070,6 +1070,8 @@ static void setVirtualSizeRandR12(ScrnInfoPtr pScrn, bool fLimitedContext)
             TRACE_LOG("cx=%u, cy=%u\n", cx, cy);
             xf86ScrnToScreen(pScrn)->width = cx;
             xf86ScrnToScreen(pScrn)->height = cy;
+	    xf86ScrnToScreen(pScrn)->mmWidth = cx * 254 / 960;
+	    xf86ScrnToScreen(pScrn)->mmHeight = cy * 254 / 960;
             adjustScreenPixmap(pScrn, cx, cy);
             vbvxSetSolarisMouseRange(cx, cy);
         }