diff --git a/zkapauthorizer.nix b/zkapauthorizer.nix
index e617ab0d98185f086a1856cf4b294b0de81c669c..bb7e5e21b46b1ab8d47e64bee5522cd01744176f 100644
--- a/zkapauthorizer.nix
+++ b/zkapauthorizer.nix
@@ -1,4 +1,5 @@
-{ buildPythonPackage, sphinx
+{ lib
+, buildPythonPackage, sphinx
 , attrs, zope_interface, aniso8601, twisted, tahoe-lafs, privacypass
 , fixtures, testtools, hypothesis, pyflakes, treq, coverage
 , hypothesisProfile ? null
@@ -15,7 +16,7 @@ buildPythonPackage rec {
   version = "0.0";
   pname = "zero-knowledge-access-pass-authorizer";
   name = "${pname}-${version}";
-  src = ./.;
+  src = lib.cleanSource ./.;
 
   outputs = [ "out" ] ++ (if collectCoverage then [ "doc" ] else [ ]);