diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -54,7 +54,7 @@ requirements = [
     "URLObject==2.3.4",
     "Routes==1.13",
     "dulwich>=0.14.1",
-    "mercurial>=2.9,<3.9",
+    "mercurial>=2.9,<4.0",
 ]
 
 if sys.version_info < (2, 7):