diff --git a/src/Year_2017/P7.py b/src/Year_2017/P7.py
index 7a1c5b5..ed9b235 100644
--- a/src/Year_2017/P7.py
+++ b/src/Year_2017/P7.py
@@ -69,7 +69,7 @@ with open("files/P7.txt") as f:
     towers = [line for line in f.read().strip().split("\n")]
 
 
-def part_1():
+def part_1() -> None:
     parents, childs = [], []
     for line in towers:
         if "->" in line: