diff --git a/pkgs/development/python-modules/mypy/extensions.nix b/pkgs/development/python-modules/mypy/extensions.nix
index e62fa4230fff..04b22e2c5438 100644
--- a/pkgs/development/python-modules/mypy/extensions.nix
+++ b/pkgs/development/python-modules/mypy/extensions.nix
@@ -1,20 +1,30 @@
-{ lib, fetchPypi, buildPythonPackage, typing, pythonOlder }:
+{ lib
+, fetchFromGitHub
+, buildPythonPackage
+, typing
+, python
+, pythonOlder
+}:
 
 buildPythonPackage rec {
   pname = "mypy-extensions";
   version = "0.4.3";
 
-  # Tests not included in pip package.
-  doCheck = false;
-
-  src = fetchPypi {
-    inherit version;
-    pname = "mypy_extensions";
-    sha256 = "2d82818f5bb3e369420cb3c4060a7970edba416647068eb4c5343488a6c604a8";
+  src = fetchFromGitHub {
+    owner = "python";
+    repo = "mypy_extensions";
+    rev = version;
+    sha256 = "sha256-JjhbxX5DBAbcs1o2fSWywz9tot792q491POXiId+NyI=";
   };
 
   propagatedBuildInputs = lib.optional (pythonOlder "3.5") typing;
 
+  checkPhase = ''
+    ${python.interpreter} -m unittest discover tests
+  '';
+
+  pythonImportsCheck = [ "mypy_extensions" ];
+
   meta = with lib; {
     description = "Experimental type system extensions for programs checked with the mypy typechecker";
     homepage = "http://www.mypy-lang.org";