diff --git a/pkgs/development/python-modules/charset-normalizer/default.nix b/pkgs/development/python-modules/charset-normalizer/default.nix
index 5137ceb0e83f..da6efe28e397 100644
--- a/pkgs/development/python-modules/charset-normalizer/default.nix
+++ b/pkgs/development/python-modules/charset-normalizer/default.nix
@@ -8,6 +8,7 @@
   pytestCheckHook,
   requests,
   setuptools,
+  withMypyc ? !isPyPy,
 }:
 
 buildPythonPackage rec {
@@ -30,9 +31,9 @@ buildPythonPackage rec {
   build-system = [
     setuptools
   ]
-  ++ lib.optional (!isPyPy) mypy;
+  ++ lib.optional (withMypyc) mypy;
 
-  env.CHARSET_NORMALIZER_USE_MYPYC = lib.optionalString (!isPyPy) "1";
+  env.CHARSET_NORMALIZER_USE_MYPYC = lib.optionalString withMypyc "1";
 
   nativeCheckInputs = [ pytestCheckHook ];