diff --git a/pkgs/development/python-modules/mock-open/default.nix b/pkgs/development/python-modules/mock-open/default.nix
index 7b6c97b8253..391ba29a98c 100644
--- a/pkgs/development/python-modules/mock-open/default.nix
+++ b/pkgs/development/python-modules/mock-open/default.nix
@@ -1,17 +1,24 @@
-{ lib, buildPythonPackage, fetchFromGitHub, pythonOlder, mock }:
+{ lib, buildPythonPackage, fetchFromGitHub, fetchpatch, pythonOlder, mock }:
 
 buildPythonPackage rec {
   pname = "mock-open";
-  version = "1.3.2";
+  version = "1.4.0";
 
   # no tests in PyPI tarball
   src = fetchFromGitHub {
     owner = "nivbend";
     repo = pname;
     rev = "v${version}";
-    sha256 = "08m8mq7wws59zir06b7dzikb6gl6plq3kk2zqrmar6922zcbnk8m";
+    sha256 = "0qlz4y8jqxsnmqg03yp9f87rmnjrvmxm5qvm6n1218gm9k5dixbm";
   };
 
+  patches = lib.optional (pythonOlder "3.0")
+    (fetchpatch {
+      name = "ascii-only.patch";
+      url = "https://github.com/das-g/mock-open/commit/521ff260da127949fe4aceff1667cba223c5b07b.patch";
+      sha256 = "0ampbhk7kwkn0q5d2h9wrflkr8fji2bybmdck4qdzw1qkslfwwrn";
+    });
+
   propagatedBuildInputs = lib.optional (pythonOlder "3.3") mock;
 
   meta = with lib; {