diff --git a/rclpy/rclpy/topic_or_service_is_hidden.py b/rclpy/rclpy/topic_or_service_is_hidden.py
index 3486532a0..876f9f8f1 100644
--- a/rclpy/rclpy/topic_or_service_is_hidden.py
+++ b/rclpy/rclpy/topic_or_service_is_hidden.py
@@ -15,7 +15,7 @@
 HIDDEN_TOPIC_PREFIX = '_'
 
 
-def topic_or_service_is_hidden(name):
+def topic_or_service_is_hidden(name: str) -> bool:
     """
     Return True if a given topic or service name is hidden, otherwise False.