Index: /trunk/src/VBox/Devices/Storage/DevAHCI.cpp
===================================================================
--- /trunk/src/VBox/Devices/Storage/DevAHCI.cpp	(revision 79670)
+++ /trunk/src/VBox/Devices/Storage/DevAHCI.cpp	(revision 79671)
@@ -2463,5 +2463,5 @@
      * handling 2nd DWORD failures on split accesses correctly. */
     int rc = PDMDevHlpMMIORegister(pDevIns, GCPhysAddress, cb, NULL /*pvUser*/,
-                                   IOMMMIO_FLAGS_READ_DWORD | IOMMMIO_FLAGS_WRITE_ONLY_DWORD_QWORD,
+                                   IOMMMIO_FLAGS_READ_DWORD | IOMMMIO_FLAGS_WRITE_DWORD_QWORD_READ_MISSING,
                                    ahciMMIOWrite, ahciMMIORead, "AHCI");
     if (RT_FAILURE(rc))