diff --git a/nix/tahoe-lafs.nix b/nix/tahoe-lafs.nix
index cc0eea479..3b54519f1 100644
--- a/nix/tahoe-lafs.nix
+++ b/nix/tahoe-lafs.nix
@@ -4,7 +4,7 @@
 , setuptools, setuptoolsTrial, pyasn1, zope_interface
 , service-identity, pyyaml, magic-wormhole, treq, appdirs
 , beautifulsoup4, eliot, autobahn, cryptography
-, html5lib
+, html5lib, future
 }:
 python.pkgs.buildPythonPackage rec {
   version = "1.14.0.dev";