diff --git a/nix/klein.nix b/nix/klein.nix
new file mode 100644
index 000000000..aa109e3d1
--- /dev/null
+++ b/nix/klein.nix
@@ -0,0 +1,18 @@
+{ lib, buildPythonPackage, fetchPypi }:
+buildPythonPackage rec {
+  pname = "klein";
+  version = "21.8.0";
+
+  src = fetchPypi {
+    sha256 = "09i1x5ppan3kqsgclbz8xdnlvzvp3amijbmdzv0kik8p5l5zswxa";
+    inherit pname version;
+  };
+
+  doCheck = false;
+
+  meta = with lib; {
+    homepage = https://github.com/twisted/klein;
+    description = "Nicer web server for Twisted";
+    license = licenses.mit;
+  };
+}
diff --git a/nix/overlays.nix b/nix/overlays.nix
index fbd0ce3bb..011d8dd6b 100644
--- a/nix/overlays.nix
+++ b/nix/overlays.nix
@@ -28,6 +28,9 @@ self: super: {
     packageOverrides = python-self: python-super: {
       # collections-extended is not part of nixpkgs at this time.
       collections-extended = python-super.pythonPackages.callPackage ./collections-extended.nix { };
+
+      # klein is not in nixpkgs 21.05, at least:
+      klein = python-super.pythonPackages.callPackage ./klein.nix { };
     };
   };
 }