diff --git a/timer.py b/timer.py
index 721b90a..872a027 100755
--- a/timer.py
+++ b/timer.py
@@ -77,7 +77,7 @@ def start_app(enddate):
             tlbl.config(fg="red")
         else:
             tlbl.configure(text=deltaStr(delta))
-        root.after(1000 - int(datetime.datetime.now().microsecond / 1000), update)
+        root.after(1000 - datetime.datetime.now().microsecond // 1000, update)
 
     root.bind("<Configure>", resize)
     root.bind("<Escape>", lambda x: root.destroy())