diff --git a/app/routes.py b/app/routes.py
index 63aeb21..b3b7c6d 100644
--- a/app/routes.py
+++ b/app/routes.py
@@ -266,7 +266,11 @@ def edit_reading(reading_id):
     if form.validate_on_submit():
         # Convert the local timestamp back to UTC for saving
         local_timestamp = form.timestamp.data
-        reading.timestamp = user_timezone.localize(local_timestamp).astimezone(utc)
+        # Ensure the local timestamp is naive before localizing
+        if local_timestamp.tzinfo is not None:
+            local_timestamp = local_timestamp.replace(tzinfo=None)
+
+        reading.timestamp = local_tz.localize(local_timestamp).astimezone(utc)
 
         reading.systolic = form.systolic.data
         reading.diastolic = form.diastolic.data