Index: /trunk/src/VBox/Main/src-server/MachineImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/src-server/MachineImpl.cpp	(revision 92538)
+++ /trunk/src/VBox/Main/src-server/MachineImpl.cpp	(revision 92539)
@@ -384,4 +384,8 @@
         for (ULONG slot = 0; slot < RT_ELEMENTS(mParallelPorts); ++slot)
             mParallelPorts[slot]->i_applyDefaults();
+
+        /* Enable the VMMDev testing feature for bootsector VMs: */
+        if (aOsType && aOsType->i_id() == "VBoxBS_64")
+            mData->pMachineConfigFile->mapExtraDataItems["VBoxInternal/Devices/VMMDev/0/Config/TestingEnabled"] = "1";
 
         /* At this point the changing of the current state modification
@@ -15473,4 +15477,13 @@
         }
     }
+
+    /* Enable the VMMDev testing feature for bootsector VMs: */
+    if (osTypeId == "VBoxBS_64")
+    {
+        rc = setExtraData("VBoxInternal/Devices/VMMDev/0/Config/TestingEnabled", "1");
+        if (FAILED(rc))
+            return rc;
+    }
+
     return S_OK;
 }