diff --git a/tilde-train.py b/tilde-train.py
index d248aa8..40fbf33 100755
--- a/tilde-train.py
+++ b/tilde-train.py
@@ -51,7 +51,7 @@ max_cars = 10 ## most cars to include in one train.
 print_train = False ## print train to file (instead of the screen scroll)
 
 train = [""]*max_y ## empty train of correct height.
-cars = []
+cars: list[list[str]] = []
 
 engine = [
   r"        ____                      ",