diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -404,11 +404,6 @@
 
     return commit(ui, repo, recordinwlock, pats, opts)
 
-
-# extracted at module level as it's required each time a file will be added
-# to dirnode class object below
-pathsep = pycompat.ossep
-
 class dirnode(object):
     """
     Represent a directory in user working copy with information required for
@@ -435,6 +430,19 @@
         """Add a file in this directory as a direct child."""
         self.files.append((filename, status))
 
+    def _splitbyroot(self, path):
+        """
+        splits the path from the first occurence of os.sep and returns a tuple
+        (rootdirectory, restofthepath)
+        """
+        #XXX: must be replaced with pathlib once we drop Py2.7
+        parentdir = os.path.dirname(path)
+        temp = path
+        while parentdir:
+            temp = parentdir
+            parentdir = os.path.dirname(parentdir)
+        return temp, path[len(temp) + 1:]
+
     def addfile(self, filename, status):
         """
         Add a file to this directory or to its direct parent directory.
@@ -446,8 +454,8 @@
 
         # the filename contains a path separator, it means it's not the direct
         # child of this directory
-        if pathsep in filename:
-            subdir, filep = filename.split(pathsep, 1)
+        if pycompat.ossep in filename:
+            subdir, filep = self._splitbyroot(filename)
 
             # does the dirnode object for subdir exists
             if subdir not in self.subdirs: