Index: /trunk/src/VBox/Frontends/VirtualBox/src/selector/graphics/details/UIGMachinePreview.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/selector/graphics/details/UIGMachinePreview.cpp	(revision 55818)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/selector/graphics/details/UIGMachinePreview.cpp	(revision 55819)
@@ -251,4 +251,11 @@
                     KGuestMonitorStatus monitorStatus = KGuestMonitorStatus_Enabled;
                     display.GetScreenResolution(0, uGuestWidth, uGuestHeight, uBpp, iOriginX, iOriginY, monitorStatus);
+                    if (uGuestWidth == 0 || uGuestHeight == 0)
+                    {
+                        AssertMsgFailed(("Acquired guest screen resolution is %dx%d\n",
+                                         uGuestWidth, uGuestHeight));
+                        break;
+                    }
+
                     double dAspectRatio = (double)uGuestWidth / uGuestHeight;
                     /* Look for the best aspect-ratio preset preset: */
@@ -515,4 +522,8 @@
 QSize UIGMachinePreview::imageAspectRatioSize(const QSize &hostSize, const QSize &guestSize)
 {
+    /* Make sure host-size and guest-size are valid: */
+    AssertReturn(!hostSize.isNull(), QSize());
+    AssertReturn(!guestSize.isNull(), hostSize);
+
     /* Calculate host/guest aspect-ratio: */
     const double dHostAspectRatio = (double)hostSize.width() / hostSize.height();