diff --git a/arztapi/APIHandler.py b/arztapi/APIHandler.py
index a54a741..d7db73d 100644
--- a/arztapi/APIHandler.py
+++ b/arztapi/APIHandler.py
@@ -239,7 +239,7 @@ class APIHandler:
             if "24:00" in date_string:
                 # Sometimes the API returns 24:00 as time, so filtering for those cases and replacing it with a minute
                 # less to work with propery input
-                date_string.replace("24:00", "23:59")
+                date_string =date_string.replace("24:00", "23:59")
 
             # Add the current year since it is not part of the original date sent by the API
             parsed_date = datetime.strptime(date_string, format_string).replace(year=datetime.now().year)