diff --git a/Makefile b/Makefile
index 07e068a..4a6fd07 100644
--- a/Makefile
+++ b/Makefile
@@ -12,7 +12,4 @@ test:
 	. venv/bin/activate; cd ./src; python -m pytest
 
 lint:
-	. venv/bin/activate; \
-	cd ./src
-	flake8 --ignore=E252,W504,W503 --max-line-length=120 . \
-	&& mypy --follow-imports=skip --ignore-missing-imports .
+	. venv/bin/activate; flake8 --ignore=E252,W504,W503 --max-line-length=120 ./src/ && mypy --follow-imports=skip --ignore-missing-imports ./src/
diff --git a/src/tests/__init__.py b/src/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/tests/test_key_derivation/test_mnemonic.py b/src/tests/test_key_derivation/test_mnemonic.py
index a676357..c155124 100644
--- a/src/tests/test_key_derivation/test_mnemonic.py
+++ b/src/tests/test_key_derivation/test_mnemonic.py
@@ -8,6 +8,7 @@ from key_derivation.mnemonic import (
 with open('tests/test_key_derivation/test_vectors/mnemonic.json', 'r') as f:
     test_vectors = load(f)
 
+
 @pytest.mark.parametrize(
     'language,language_test_vectors',
     [(a, b) for a, b in test_vectors.items()]
diff --git a/src/utils/crypto.py b/src/utils/crypto.py
index b5b2124..2f45ce2 100644
--- a/src/utils/crypto.py
+++ b/src/utils/crypto.py
@@ -25,8 +25,8 @@ def scrypt(*, password: str, salt: str, n: int, r: int, p: int, dklen: int) -> b
 def PBKDF2(*, password: str, salt: bytes, dklen: int, c: int, prf: str) -> bytes:
     assert('sha' in prf)
     _hash = _sha256 if 'sha256' in prf else _sha512
-    password = password.encode("utf-8")
-    res = _PBKDF2(password=password, salt=salt, dkLen=dklen, count=c, hmac_hash_module=_hash)
+    password_bytes = password.encode("utf-8")
+    res = _PBKDF2(password=password_bytes, salt=salt, dkLen=dklen, count=c, hmac_hash_module=_hash)  # type: ignore
     return res if isinstance(res, bytes) else res[0]  # PyCryptodome can return Tuple[bytes]