Index: /trunk/src/VBox/VMM/CPUM.cpp
===================================================================
--- /trunk/src/VBox/VMM/CPUM.cpp	(revision 26663)
+++ /trunk/src/VBox/VMM/CPUM.cpp	(revision 26664)
@@ -628,5 +628,5 @@
     rc = CFGMR3QueryBoolDef(pCpumCfg, "MWaitExtensions", &fMWaitExtensions, false); AssertRCReturn(rc, rc);
     if (fMWaitExtensions)
-        pCPUM->aGuestCpuIdStd[5].ecx = 3;
+        pCPUM->aGuestCpuIdStd[5].ecx = X86_CPUID_MWAIT_ECX_EXT | X86_CPUID_MWAIT_ECX_BREAKIRQIF0;
 
     /*