Index: /trunk/src/VBox/Devices/Bus/DevPciIch9.cpp
===================================================================
--- /trunk/src/VBox/Devices/Bus/DevPciIch9.cpp	(revision 65323)
+++ /trunk/src/VBox/Devices/Bus/DevPciIch9.cpp	(revision 65324)
@@ -1721,5 +1721,8 @@
                 || uNew >= _4G)
             {
-                if (f64Bit)
+                /* Only prefetchable regions can be placed above 4GB, as the
+                 * address decoder for non-prefetchable addresses in bridges
+                 * is limited to 32 bits. */
+                if (f64Bit && fPrefetch)
                 {
                     /* Map a 64-bit region above 4GB. */