diff --git a/pkgs/by-name/mu/mutmut/package.nix b/pkgs/by-name/mu/mutmut/package.nix
index f505a2c5f204..f75af0144ac5 100644
--- a/pkgs/by-name/mu/mutmut/package.nix
+++ b/pkgs/by-name/mu/mutmut/package.nix
@@ -1,50 +1,45 @@
 {
   lib,
   fetchFromGitHub,
-  python3,
+  mutmut,
+  python3Packages,
   testers,
 }:
+python3Packages.buildPythonApplication rec {
+  pname = "mutmut";
+  version = "2.2.0";
 
-let
-  self =
-    with python3.pkgs;
-    buildPythonApplication rec {
-      pname = "mutmut";
-      version = "2.2.0";
+  src = fetchFromGitHub {
+    repo = pname;
+    owner = "boxed";
+    rev = "refs/tags/${version}";
+    hash = "sha256-G+OL/9km2iUeZ1QCpU73CIWVWMexcs3r9RdCnAsESnY=";
+  };
 
-      src = fetchFromGitHub {
-        repo = pname;
-        owner = "boxed";
-        rev = "refs/tags/${version}";
-        hash = "sha256-G+OL/9km2iUeZ1QCpU73CIWVWMexcs3r9RdCnAsESnY=";
-      };
+  postPatch = ''
+    substituteInPlace requirements.txt --replace 'junit-xml==1.8' 'junit-xml==1.9'
+  '';
 
-      postPatch = ''
-        substituteInPlace requirements.txt --replace 'junit-xml==1.8' 'junit-xml==1.9'
-      '';
+  disabled = python3Packages.pythonOlder "3.7";
 
-      disabled = pythonOlder "3.7";
+  doCheck = false;
 
-      doCheck = false;
+  propagatedBuildInputs = with python3Packages; [
+    click
+    glob2
+    parso
+    pony
+    junit-xml
+  ];
 
-      propagatedBuildInputs = [
-        click
-        glob2
-        parso
-        pony
-        junit-xml
-      ];
+  passthru.tests.version = testers.testVersion { package = mutmut; };
 
-      passthru.tests.version = testers.testVersion { package = self; };
-
-      meta = with lib; {
-        description = "mutation testing system for Python, with a strong focus on ease of use";
-        mainProgram = "mutmut";
-        homepage = "https://github.com/boxed/mutmut";
-        changelog = "https://github.com/boxed/mutmut/blob/${version}/HISTORY.rst";
-        license = licenses.bsd3;
-        maintainers = with maintainers; [ synthetica ];
-      };
-    };
-in
-self
+  meta = with lib; {
+    description = "mutation testing system for Python, with a strong focus on ease of use";
+    mainProgram = "mutmut";
+    homepage = "https://github.com/boxed/mutmut";
+    changelog = "https://github.com/boxed/mutmut/blob/${version}/HISTORY.rst";
+    license = licenses.bsd3;
+    maintainers = with maintainers; [ synthetica ];
+  };
+}