diff --git a/examples/__init__.py b/examples/__init__.py
index b49f3dd..d1fbea4 100644
--- a/examples/__init__.py
+++ b/examples/__init__.py
@@ -1,8 +1,10 @@
+import collections.abc as abc
+
 DEMOS = {}
 
 
-def demo(func):
-    def w(banner=True):
+def demo(func) -> abc.Callable[[], None]:
+    def w(banner=True) -> None:
         if banner:
             print("-" * 80)
             print(func.__name__)