Index: /trunk/src/VBox/Runtime/common/vfs/vfsbase.cpp
===================================================================
--- /trunk/src/VBox/Runtime/common/vfs/vfsbase.cpp	(revision 66575)
+++ /trunk/src/VBox/Runtime/common/vfs/vfsbase.cpp	(revision 66576)
@@ -1645,6 +1645,5 @@
 
 
-RTDECL(int)         RTVfsIsRangeInUse(RTVFS hVfs, uint64_t off, size_t cb,
-                                      bool *pfUsed)
+RTDECL(int)         RTVfsIsRangeInUse(RTVFS hVfs, uint64_t off, size_t cb, bool *pfUsed)
 {
     RTVFSINTERNAL *pThis = hVfs;
@@ -1652,4 +1651,6 @@
     AssertReturn(pThis->uMagic == RTVFS_MAGIC, VERR_INVALID_HANDLE);
 
+    if (!pThis->pOps->pfnIsRangeInUse)
+        return VERR_NOT_SUPPORTED;
     RTVfsLockAcquireWrite(pThis->Base.hLock);
     int rc = pThis->pOps->pfnIsRangeInUse(pThis->Base.pvThis, off, cb, pfUsed);