Index: /trunk/src/VBox/Devices/Storage/DrvHostBase.cpp
===================================================================
--- /trunk/src/VBox/Devices/Storage/DrvHostBase.cpp	(revision 24007)
+++ /trunk/src/VBox/Devices/Storage/DrvHostBase.cpp	(revision 24008)
@@ -2005,5 +2005,5 @@
     /* name to open & watch for */
 #ifdef RT_OS_WINDOWS
-    int iBit = toupper(pThis->pszDevice[0]) - 'A';
+    int iBit = RT_C_TO_UPPER(pThis->pszDevice[0]) - 'A';
     if (    iBit > 'Z' - 'A'
         ||  pThis->pszDevice[1] != ':'