diff --git a/dlls/shlwapi/path.c b/dlls/shlwapi/path.c
index 3c07bb8..89a3572 100644
--- a/dlls/shlwapi/path.c
+++ b/dlls/shlwapi/path.c
@@ -538,17 +538,25 @@
  *
  * See PathGetDriveNumberA.
  */
-int WINAPI PathGetDriveNumberW(LPCWSTR lpszPath)
+int WINAPI PathGetDriveNumberW(const WCHAR *path)
 {
-  TRACE ("(%s)\n",debugstr_w(lpszPath));
+    WCHAR drive;
 
-  if (lpszPath)
-  {
-      WCHAR tl = tolowerW(lpszPath[0]);
-      if (tl >= 'a' && tl <= 'z' && lpszPath[1] == ':')
-          return tl - 'a';
-  }
-  return -1;
+    static const WCHAR nt_prefixW[] = {'\\','\\','?','\\'};
+
+    TRACE("(%s)\n", debugstr_w(path));
+
+    if (!path)
+        return -1;
+
+    if (!strncmpW(path, nt_prefixW, 4))
+        path += 4;
+
+    drive = tolowerW(path[0]);
+    if (drive < 'a' || drive > 'z' || path[1] != ':')
+        return -1;
+
+    return drive - 'a';
 }
 
 /*************************************************************************
diff --git a/dlls/shlwapi/tests/path.c b/dlls/shlwapi/tests/path.c
index f780a78..57fdfdd 100644
--- a/dlls/shlwapi/tests/path.c
+++ b/dlls/shlwapi/tests/path.c
@@ -1429,6 +1429,11 @@
     static const CHAR test2A[] = "file:////b:\\test.file";
     static const CHAR test3A[] = "file:///c:\\test.file";
     static const CHAR test4A[] = "file:\\\\c:\\test.file";
+    static const CHAR test5A[] = "\\\\?\\C:\\dir\\file.txt";
+    static const WCHAR test1W[] =
+        {'a',':','\\',0};
+    static const WCHAR test5W[] =
+        {'\\','\\','?','\\','C',':','\\','d','i','r','\\','f','i','l','e',0};
     int ret;
 
     SetLastError(0xdeadbeef);
@@ -1438,12 +1443,19 @@
 
     ret = PathGetDriveNumberA(test1A);
     ok(ret == 0, "got %d\n", ret);
+    ret = PathGetDriveNumberW(test1W);
+    ok(ret == 0, "got %d\n", ret);
     ret = PathGetDriveNumberA(test2A);
     ok(ret == -1, "got %d\n", ret);
     ret = PathGetDriveNumberA(test3A);
     ok(ret == -1, "got %d\n", ret);
     ret = PathGetDriveNumberA(test4A);
     ok(ret == -1, "got %d\n", ret);
+
+    ret = PathGetDriveNumberA(test5A);
+    ok(ret == -1, "got %d\n", ret);
+    ret = PathGetDriveNumberW(test5W);
+    ok(ret == 2 || broken(ret == -1) /* winxp */, "got = %d\n", ret);
 }
 
 static void test_PathUnExpandEnvStrings(void)