diff --git a/src/server/BreCal/schemas/model.py b/src/server/BreCal/schemas/model.py
index 7bc6b5e..9bee8e3 100644
--- a/src/server/BreCal/schemas/model.py
+++ b/src/server/BreCal/schemas/model.py
@@ -22,8 +22,8 @@ def _format_datetime(value):
         return None
     if isinstance(value, datetime.datetime):
         if value.tzinfo is None or value.tzinfo.utcoffset(value) is None:
-            return value.isoformat() + "Z"
-        return value.isoformat()
+            return value.isoformat()
+        return value.astimezone().replace(tzinfo=None).isoformat()
     return value
 
 def obj_dict(obj):