diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8a66388..fbc8183 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## 2.0.3 - August 2, 2021
+- stricter type checking
+
 ## 2.0.2 - July 25, 2021
 - add py.typed file to indicate to mypy that the library is fully type annotated.
 
diff --git a/business/__init__.py b/business/__init__.py
index f22b97c..c7f65b5 100644
--- a/business/__init__.py
+++ b/business/__init__.py
@@ -1,7 +1,8 @@
 """Init."""
+# mypy: ignore-errors
 
 
-def get_version():
+def get_version() -> str:
     """Get package version."""
     try:
         from importlib.metadata import version
diff --git a/business/calendar.py b/business/calendar.py
index 5135fe8..29d77c9 100644
--- a/business/calendar.py
+++ b/business/calendar.py
@@ -3,7 +3,7 @@
 import logging
 import os
 from threading import RLock
-from typing import List, Optional, Union
+from typing import Any, Dict, Generic, List, Optional, TypeVar, Union
 
 import yaml
 from dateutil.parser import parse as dateutil_parse
@@ -12,23 +12,24 @@
 
 day_interval = datetime.timedelta(days=1)
 INPUT_TYPES = Union[str, datetime.date]
+T = TypeVar('T')
 
 
-class Mutex:
+class Mutex(Generic[T]):
     """Helper class for thread-safe locking."""
 
-    def __init__(self, obj):
+    def __init__(self, obj: T) -> None:
         """Initialise reentrant lock."""
         super().__init__()
         self.__obj = obj
         self.lock = RLock()
 
-    def __enter__(self):
+    def __enter__(self) -> T:
         """Acquire lock on entering."""
         self.lock.acquire()
         return self.__obj
 
-    def __exit__(self, *args, **kwargs):
+    def __exit__(self, *args: Any, **kwargs: Any) -> None:
         """Release lock on exit."""
         self.lock.release()
 
@@ -36,7 +37,7 @@ def __exit__(self, *args, **kwargs):
 class Calendar:
     """Calendar class."""
 
-    _cache = Mutex(dict())
+    _cache: Mutex[Dict[str, "Calendar"]] = Mutex(dict())
 
     load_paths: List[str] = []
 
@@ -68,7 +69,7 @@ def __init__(
                 raise ValueError(f"Extra working dates cannot be on working days: {d}")
 
     @classmethod
-    def load(cls, calendar_str: str):
+    def load(cls, calendar_str: str) -> "Calendar":
         """Load a scheme calendar YAML file.
 
         >>> %timeit -n 100 Calendar.load('bacs')
@@ -105,7 +106,7 @@ def load(cls, calendar_str: str):
         )
 
     @classmethod
-    def load_cache(cls, calendar_str: str):
+    def load_cache(cls, calendar_str: str) -> "Calendar":
         """Load a scheme calendar YAML file with cache.
 
         >>> %timeit Calendar.load_cache('bacs')
diff --git a/pyproject.toml b/pyproject.toml
index b1e1a43..7599c8d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "business-python"
-version = "2.0.2"
+version = "2.0.3"
 description = "Date calculations based on business calendars."
 authors = ["GoCardless <engineering@gocardless.com>"]
 readme = "README.md"
@@ -53,3 +53,6 @@ target-version = ['py36']
 [build-system]
 requires = ["poetry-core>=1.0.0"]
 build-backend = "poetry.core.masonry.api"
+
+[tool.mypy]
+strict = true