Index: /trunk/src/VBox/Main/src-client/ConsoleImpl2.cpp
===================================================================
--- /trunk/src/VBox/Main/src-client/ConsoleImpl2.cpp	(revision 66102)
+++ /trunk/src/VBox/Main/src-client/ConsoleImpl2.cpp	(revision 66103)
@@ -3223,7 +3223,11 @@
                 InsertConfigInteger(pCfg,  "McfgLength", cbMcfgLength);
                 /* 64-bit prefetch window root resource:
-                 * Only for ICH9 and if PAE or Long Mode is enabled */
-                if (fEnablePAE || fIsGuest64Bit)
-                    InsertConfigInteger(pCfg,  "PciPref64Enabled", 1);
+                 * Only for ICH9 and if PAE or Long Mode is enabled.
+                 * And only with hardware virtualization (@bugref:5454). */
+                if (   (fEnablePAE || fIsGuest64Bit)
+                    && fSupportsHwVirtEx /* HwVirt needs to be supported by the host
+                                            otherwise VMM falls back to raw mode */
+                    && fHMEnabled        /* HwVirt needs to be enabled in VM config */)
+                        InsertConfigInteger(pCfg,  "PciPref64Enabled", 1);
             }
             InsertConfigInteger(pCfg,  "HostBusPciAddress", uHbcPCIAddress);