Index: /trunk/src/VBox/VMM/VMMAll/PGMAllBth.h
===================================================================
--- /trunk/src/VBox/VMM/VMMAll/PGMAllBth.h	(revision 19788)
+++ /trunk/src/VBox/VMM/VMMAll/PGMAllBth.h	(revision 19789)
@@ -1221,5 +1221,5 @@
                     PGM_BTH_NAME(SyncPageWorkerTrackDeref)(pShwPage, pPT->a[iPTEDst].u & SHW_PTE_PG_MASK);
 #  endif
-                    pPT->a[iPTEDst].u = 0;
+                    ASMAtomicWriteSize(&pPT->a[iPTEDst], 0);
                 }
 # else /* Syncing it here isn't 100% safe and it's probably not worth spending time syncing it. */