diff --git a/mercurial/httpconnection.py b/mercurial/httpconnection.py
--- a/mercurial/httpconnection.py
+++ b/mercurial/httpconnection.py
@@ -22,8 +22,9 @@ from mercurial.i18n import _
 class httpsendfile(object):
     """This is a wrapper around the objects returned by python's "open".
 
-    Its purpose is to send file-like objects via HTTP and, to do so, it
-    defines a __len__ attribute to feed the Content-Length header.
+    Its purpose is to send file-like objects via HTTP.
+    It do however not define a __len__ attribute because the length
+    might be more than Py_ssize_t can handle.
     """
 
     def __init__(self, ui, *args, **kwargs):
@@ -35,9 +36,9 @@ class httpsendfile(object):
         self.seek = self._data.seek
         self.close = self._data.close
         self.write = self._data.write
-        self._len = os.fstat(self._data.fileno()).st_size
+        self.length = os.fstat(self._data.fileno()).st_size
         self._pos = 0
-        self._total = self._len / 1024 * 2
+        self._total = self.length / 1024 * 2
 
     def read(self, *args, **kwargs):
         try:
@@ -54,9 +55,6 @@ class httpsendfile(object):
                          unit=_('kb'), total=self._total)
         return ret
 
-    def __len__(self):
-        return self._len
-
 # moved here from url.py to avoid a cycle
 def readauthforuri(ui, uri, user):
     # Read configuration
diff --git a/mercurial/httprepo.py b/mercurial/httprepo.py
--- a/mercurial/httprepo.py
+++ b/mercurial/httprepo.py
@@ -74,9 +74,14 @@ class httprepository(wireproto.wirerepos
         if cmd == 'pushkey':
             args['data'] = ''
         data = args.pop('data', None)
+        size = 0
+        if util.safehasattr(data, 'length'):
+            size = data.length
+        elif data is not None:
+            size = len(data)
         headers = args.pop('headers', {})
 
-        if data and self.ui.configbool('ui', 'usehttp2', False):
+        if size and self.ui.configbool('ui', 'usehttp2', False):
             headers['Expect'] = '100-Continue'
             headers['X-HgHttp2'] = '1'
 
@@ -105,9 +110,6 @@ class httprepository(wireproto.wirerepos
         cu = "%s%s" % (self._url, qs)
         req = urllib2.Request(cu, data, headers)
         if data is not None:
-            # len(data) is broken if data doesn't fit into Py_ssize_t
-            # add the header ourself to avoid OverflowError
-            size = data.__len__()
             self.ui.debug("sending %s bytes\n" % size)
             req.add_unredirected_header('Content-Length', '%d' % size)
         try:
diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -24,6 +24,10 @@ import imp, socket, urllib
 def sha1(s):
     return _fastsha1(s)
 
+_notset = object()
+def safehasattr(thing, attr):
+    return getattr(thing, attr, _notset) is not _notset
+
 def _fastsha1(s):
     # This function will import sha1 from hashlib or sha (whichever is
     # available) and overwrite itself with it on the first call.