diff --git a/docs/index.rst b/docs/index.rst
index 6ff500d1..9fca971c 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -106,7 +106,7 @@ Key features of the ``Dependency Injector``:
 
 
    @inject
-   def main(service: Service = Provide[Container.service]):
+   def main(service: Service = Provide[Container.service]) -> None:
        ...
 
 
diff --git a/examples/demo/after.py b/examples/demo/after.py
index 92240644..dad25cec 100644
--- a/examples/demo/after.py
+++ b/examples/demo/after.py
@@ -3,18 +3,18 @@ import os
 
 class ApiClient:
 
-    def __init__(self, api_key: str, timeout: int):
+    def __init__(self, api_key: str, timeout: int) -> None:
         self.api_key = api_key  # <-- dependency is injected
         self.timeout = timeout  # <-- dependency is injected
 
 
 class Service:
 
-    def __init__(self, api_client: ApiClient):
+    def __init__(self, api_client: ApiClient) -> None:
         self.api_client = api_client  # <-- dependency is injected
 
 
-def main(service: Service):  # <-- dependency is injected
+def main(service: Service) -> None:  # <-- dependency is injected
     ...
 
 
@@ -23,7 +23,7 @@ if __name__ == "__main__":
         service=Service(
             api_client=ApiClient(
                 api_key=os.getenv("API_KEY"),
-                timeout=os.getenv("TIMEOUT"),
+                timeout=int(os.getenv("TIMEOUT")),
             ),
         ),
     )
diff --git a/examples/demo/with_di.py b/examples/demo/with_di.py
index bf154976..58114e55 100644
--- a/examples/demo/with_di.py
+++ b/examples/demo/with_di.py
@@ -23,7 +23,7 @@ class Container(containers.DeclarativeContainer):
 
 
 @inject
-def main(service: Service = Provide[Container.service]):
+def main(service: Service = Provide[Container.service]) -> None:
     ...