diff --git a/pkgs/python-packages.nix b/pkgs/python-packages.nix
--- a/pkgs/python-packages.nix
+++ b/pkgs/python-packages.nix
@@ -316,11 +316,11 @@ self: super: {
     };
   };
   "mercurial" = super.buildPythonPackage {
-    name = "mercurial-4.6.2";
+    name = "mercurial-4.9";
     doCheck = false;
     src = fetchurl {
-      url = "https://files.pythonhosted.org/packages/d9/fb/c7ecf2b7fd349878dbf45b8390b8db735cef73d49dd9ce8a364b4ca3a846/mercurial-4.6.2.tar.gz";
-      sha256 = "1bv6wgcdx8glihjjfg22khhc52mclsn4kwfqvzbzlg0b42h4xl0w";
+      url = "https://files.pythonhosted.org/packages/1a/bb/fa36ada5f8d05651d30edeeb1b8dc7bf797ea701a77e4842c334246c912d/mercurial-4.9.tar.gz";
+      sha256 = "01ig0464cvy9d87rn274g39frxr0p5q4lxf1xn5k3m24grf0qq0g";
     };
     meta = {
       license = [ pkgs.lib.licenses.gpl1 pkgs.lib.licenses.gpl2Plus ];
diff --git a/requirements.txt b/requirements.txt
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,7 +11,7 @@ hgsubversion==1.9.3
 hg-evolve==8.0.1
 mako==1.0.7
 markupsafe==1.1.0
-mercurial==4.6.2
+mercurial==4.9.0
 msgpack-python==0.5.6
 
 pastedeploy==2.0.1
diff --git a/vcsserver/hg.py b/vcsserver/hg.py
--- a/vcsserver/hg.py
+++ b/vcsserver/hg.py
@@ -33,7 +33,7 @@ from vcsserver.base import RepoFactory, 
 from vcsserver.hgcompat import (
     archival, bin, clone, config as hgconfig, diffopts, hex,
     hg_url as url_parser, httpbasicauthhandler, httpdigestauthhandler,
-    makepeer, localrepository, match, memctx, exchange, memfilectx, nullrev,
+    makepeer, instance, match, memctx, exchange, memfilectx, nullrev,
     patch, peer, revrange, ui, hg_tag, Abort, LookupError, RepoError,
     RepoLookupError, InterventionRequired, RequirementError)
 
@@ -114,7 +114,7 @@ class MercurialFactory(RepoFactory):
 
     def _create_repo(self, wire, create):
         baseui = self._create_config(wire["config"])
-        return localrepository(baseui, wire["path"], create)
+        return instance(baseui, wire["path"], create)
 
 
 class HgRemote(object):
@@ -266,14 +266,14 @@ class HgRemote(object):
         ctx = repo[revision]
         return ctx.description()
 
-    @reraise_safe_exceptions
-    def ctx_diff(
-            self, wire, revision, git=True, ignore_whitespace=True, context=3):
-        repo = self._factory.repo(wire)
-        ctx = repo[revision]
-        result = ctx.diff(
-            git=git, ignore_whitespace=ignore_whitespace, context=context)
-        return list(result)
+    # @reraise_safe_exceptions
+    # def ctx_diff(
+    #         self, wire, revision, git=True, ignore_whitespace=True, context=3):
+    #     repo = self._factory.repo(wire)
+    #     ctx = repo[revision]
+    #     result = ctx.diff(
+    #         git=git, ignore_whitespace=ignore_whitespace, context=context)
+    #     return list(result)
 
     @reraise_safe_exceptions
     def ctx_files(self, wire, revision):
@@ -638,7 +638,7 @@ class HgRemote(object):
         # case when we want to compare two independent repositories
         if other_path and other_path != wire["path"]:
             baseui = self._factory._create_config(wire["config"])
-            repo = unionrepo.unionrepository(baseui, other_path, wire["path"])
+            repo = unionrepo.makeunionrepository(baseui, other_path, wire["path"])
         else:
             repo = self._factory.repo(wire)
         return list(repo.revs(rev_spec, *args))
diff --git a/vcsserver/hgcompat.py b/vcsserver/hgcompat.py
--- a/vcsserver/hgcompat.py
+++ b/vcsserver/hgcompat.py
@@ -44,7 +44,7 @@ from mercurial.error import (
     LookupError, RepoError, RepoLookupError, Abort, InterventionRequired,
     RequirementError)
 from mercurial.hgweb import hgweb_mod
-from mercurial.localrepo import localrepository
+from mercurial.localrepo import instance
 from mercurial.match import match
 from mercurial.mdiff import diffopts
 from mercurial.node import bin, hex