diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 007fc0a..af40d41 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -3,6 +3,19 @@ name: Test
 on: [push, pull_request]
 
 jobs:
+  mypy:
+    name: mypy
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+      - name: Install dependencies
+        run: pip install mypy cryptography types-requests
+      - name: Run mypy
+        run: mypy pyfritzhome
+      
   tests:
     name: Python ${{ matrix.python-version }} on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
diff --git a/pyfritzhome/devicetypes/fritzhomeentitybase.py b/pyfritzhome/devicetypes/fritzhomeentitybase.py
index 7a8e437..b15278f 100644
--- a/pyfritzhome/devicetypes/fritzhomeentitybase.py
+++ b/pyfritzhome/devicetypes/fritzhomeentitybase.py
@@ -1,4 +1,5 @@
 """The entity base class."""
+
 # -*- coding: utf-8 -*-
 
 from __future__ import print_function
@@ -16,8 +17,8 @@ class FritzhomeEntityBase(ABC):
     """The Fritzhome Entity class."""
 
     _fritz = None
-    ain: str = None
-    _functionsbitmask = None
+    ain: str
+    _functionsbitmask: int = 0
     supported_features = None
 
     def __init__(self, fritz=None, node=None):
diff --git a/pyfritzhome/fritzhome.py b/pyfritzhome/fritzhome.py
index da1972b..0488904 100644
--- a/pyfritzhome/fritzhome.py
+++ b/pyfritzhome/fritzhome.py
@@ -16,7 +16,7 @@
 from .errors import InvalidError, LoginError, NotLoggedInError
 from .fritzhomedevice import FritzhomeDevice
 from .fritzhomedevice import FritzhomeTemplate
-from typing import Dict
+from typing import Dict, Optional
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -26,8 +26,8 @@ class Fritzhome(object):
 
     _sid = None
     _session = None
-    _devices: Dict[str, FritzhomeDevice] = None
-    _templates: Dict[str, FritzhomeTemplate] = None
+    _devices: Optional[Dict[str, FritzhomeDevice]] = None
+    _templates: Optional[Dict[str, FritzhomeTemplate]] = None
 
     def __init__(self, host, user, password, ssl_verify=True):
         """Create a fritzhome object."""