diff --git a/msvcrt.pyi b/msvcrt.pyi
new file mode 100644
index 0000000..73c309a
--- /dev/null
+++ b/msvcrt.pyi
@@ -0,0 +1,7 @@
+LK_LOCK: int
+LK_NBLCK: int
+LK_NBRLCK: int
+LK_RLCK: int
+LK_UNLCK: int
+
+def locking(file: int, mode: int, lock_length: int) -> int: ...
diff --git a/portalocker/exceptions.py b/portalocker/exceptions.py
index 0a815b9..0a8594d 100644
--- a/portalocker/exceptions.py
+++ b/portalocker/exceptions.py
@@ -1,10 +1,18 @@
+import typing
+
+
 class BaseLockException(Exception):
     # Error codes:
     LOCK_FAILED = 1
 
-    def __init__(self, *args, fh=None, **kwargs):
+    def __init__(
+        self,
+        *args: typing.Any,
+        fh: typing.Optional[typing.IO] = None,
+        **kwargs: typing.Any,
+    ) -> None:
         self.fh = fh
-        Exception.__init__(self, *args, **kwargs)
+        Exception.__init__(self, *args)
 
 
 class LockException(BaseLockException):
diff --git a/portalocker/redis.py b/portalocker/redis.py
index 9d34b24..08dbd4a 100644
--- a/portalocker/redis.py
+++ b/portalocker/redis.py
@@ -18,7 +18,7 @@
 DEFAULT_THREAD_SLEEP_TIME = 0.1
 
 
-class PubSubWorkerThread(client.PubSubWorkerThread):
+class PubSubWorkerThread(client.PubSubWorkerThread):  # type: ignore
 
     def run(self):
         try:
diff --git a/portalocker/utils.py b/portalocker/utils.py
index aefe299..b50de3e 100644
--- a/portalocker/utils.py
+++ b/portalocker/utils.py
@@ -28,7 +28,7 @@
 Filename = typing.Union[str, pathlib.Path]
 
 
-def coalesce(*args, test_value=None):
+def coalesce(*args: typing.Any, test_value: typing.Any = None) -> typing.Any:
     '''Simple coalescing function that returns the first value that is not
     equal to the `test_value`. Or `None` if no value is valid. Usually this
     means that the last given value is the default value.
@@ -56,7 +56,8 @@ def coalesce(*args, test_value=None):
 
 
 @contextlib.contextmanager
-def open_atomic(filename: Filename, binary: bool = True):
+def open_atomic(filename: Filename, binary: bool = True) \
+        -> typing.Iterator[typing.IO]:
     '''Open a file for atomic writing. Instead of locking this method allows
     you to write the entire file and move it to the actual location. Note that
     this makes the assumption that a rename is atomic on your platform which
@@ -129,21 +130,23 @@ def acquire(
             fail_when_locked: bool = None):
         return NotImplemented
 
-    def _timeout_generator(self, timeout, check_interval):
-        timeout = coalesce(timeout, self.timeout, 0.0)
-        check_interval = coalesce(check_interval, self.check_interval, 0.0)
+    def _timeout_generator(self, timeout: typing.Optional[float],
+                           check_interval: typing.Optional[float]) \
+            -> typing.Iterator[int]:
+        f_timeout = coalesce(timeout, self.timeout, 0.0)
+        f_check_interval = coalesce(check_interval, self.check_interval, 0.0)
 
         yield 0
         i = 0
 
         start_time = time.perf_counter()
-        while start_time + timeout > time.perf_counter():
+        while start_time + f_timeout > time.perf_counter():
             i += 1
             yield i
 
             # Take low lock checks into account to stay within the interval
             since_start_time = time.perf_counter() - start_time
-            time.sleep(max(0.001, (i * check_interval) - since_start_time))
+            time.sleep(max(0.001, (i * f_check_interval) - since_start_time))
 
     @abc.abstractmethod
     def release(self):
@@ -152,8 +155,13 @@ def release(self):
     def __enter__(self):
         return self.acquire()
 
-    def __exit__(self, type_, value, tb):
+    def __exit__(self,
+                 exc_type: typing.Optional[typing.Type[BaseException]],
+                 exc_value: typing.Optional[BaseException],
+                 traceback: typing.Any,  # Should be typing.TracebackType
+                 ) -> typing.Optional[bool]:
         self.release()
+        return None
 
     def __delete__(self, instance):
         instance.release()
diff --git a/setup.py b/setup.py
index 055a458..8b532ac 100644
--- a/setup.py
+++ b/setup.py
@@ -128,7 +128,7 @@ def run(self):
         author_email=about['__email__'],
         url=about['__url__'],
         license='PSF',
-        package_data=dict(portalocker=['py.typed']),
+        package_data=dict(portalocker=['py.typed', 'msvcrt.pyi']),
         packages=setuptools.find_packages(exclude=[
             'examples', 'portalocker_tests']),
         # zip_safe=False,
diff --git a/tox.ini b/tox.ini
index 0274dfb..84454fa 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,6 +14,11 @@ basepython =
 deps = -e{toxinidir}[tests,redis]
 commands = python -m pytest {posargs}
 
+[testenv:mypy]
+basepython = python3
+deps = mypy
+commands = mypy {toxinidir}/portalocker
+
 [testenv:flake8]
 basepython = python3
 deps = flake8