diff --git a/src/aleph/sdk/client/authenticated_http.py b/src/aleph/sdk/client/authenticated_http.py
index 3635919d..da7f80f7 100644
--- a/src/aleph/sdk/client/authenticated_http.py
+++ b/src/aleph/sdk/client/authenticated_http.py
@@ -1,3 +1,4 @@
+import datetime
 import hashlib
 import json
 import logging
@@ -50,6 +51,16 @@
     magic = None  # type:ignore
 
 
+def extended_json_encoder(obj: Any) -> str:
+    if (
+        isinstance(obj, datetime.datetime)
+        or isinstance(obj, datetime.date)
+        or isinstance(obj, datetime.time)
+    ):
+        return obj.isoformat()  # or any other format you prefer
+    return pydantic_encoder(obj)
+
+
 class AuthenticatedAlephHttpClient(AlephHttpClient, AuthenticatedAlephClient):
     account: Account
 
@@ -604,7 +615,7 @@ async def _prepare_aleph_message(
 
         # Use the Pydantic encoder to serialize types like UUID, datetimes, etc.
         item_content: str = json.dumps(
-            content, separators=(",", ":"), default=pydantic_encoder
+            content, separators=(",", ":"), default=extended_json_encoder
         )
 
         if allow_inlining and (len(item_content) < settings.MAX_INLINE_SIZE):