diff --git a/strings/aho_corasick.py b/strings/aho_corasick.py
index b9a6a80728f6..fa5ff0422008 100644
--- a/strings/aho_corasick.py
+++ b/strings/aho_corasick.py
@@ -4,7 +4,7 @@
 
 
 class Automaton:
-    def __init__(self, keywords: list[str]):
+    def __init__(self, keywords: list[str]) -> None:
         self.adlist: list[dict] = list()
         self.adlist.append(
             {"value": "", "next_states": [], "fail_state": 0, "output": []}