diff --git a/pkgs/development/python-modules/stem/default.nix b/pkgs/development/python-modules/stem/default.nix
index 32e4bab5afc..c607d45e170 100644
--- a/pkgs/development/python-modules/stem/default.nix
+++ b/pkgs/development/python-modules/stem/default.nix
@@ -12,6 +12,8 @@ buildPythonPackage rec {
   postPatch = ''
     rm test/unit/installation.py
     sed -i "/test.unit.installation/d" test/settings.cfg
+    # https://github.com/torproject/stem/issues/56
+    sed -i '/MOCK_VERSION/d' run_tests.py
   '';
 
   checkInputs = [ mock ];