diff --git a/pkgs/development/python-modules/fs/default.nix b/pkgs/development/python-modules/fs/default.nix
index f67bb186ab6f..1d9031fabc6b 100644
--- a/pkgs/development/python-modules/fs/default.nix
+++ b/pkgs/development/python-modules/fs/default.nix
@@ -8,7 +8,6 @@
   psutil,
   pyftpdlib,
   pytestCheckHook,
-  pythonAtLeast,
   pythonOlder,
   pytz,
   setuptools,
@@ -27,6 +26,12 @@ buildPythonPackage rec {
     hash = "sha256-rpfH1RIT9LcLapWCklMCiQkN46fhWEHhCPvhRPBp0xM=";
   };
 
+  postPatch = ''
+    # https://github.com/PyFilesystem/pyfilesystem2/pull/591
+    substituteInPlace tests/test_ftpfs.py \
+      --replace ThreadedTestFTPd FtpdThreadWrapper
+  '';
+
   build-system = [ setuptools ];
 
   dependencies = [