diff --git a/codecarbon/core/api_client.py b/codecarbon/core/api_client.py
index eaef94a53..a435e007e 100644
--- a/codecarbon/core/api_client.py
+++ b/codecarbon/core/api_client.py
@@ -8,7 +8,7 @@
 # from httpx import AsyncClient
 import dataclasses
 import json
-from datetime import timedelta, tzinfo
+from datetime import datetime, timedelta, tzinfo
 
 import requests
 
@@ -28,6 +28,24 @@ def get_datetime_with_timezone():
     return str(arrow.now().isoformat())
 
 
+def get_measurement_timestamp(timestamp=None):
+    """
+    Return the time the measurement was taken, as an offset-aware ISO string.
+
+    EmissionsData.timestamp is naive local time, so it is localised here.
+    Falls back to now for hand-built payloads without a timestamp.
+    """
+    if timestamp:
+        try:
+            return datetime.fromisoformat(timestamp).astimezone().isoformat()
+        except (TypeError, ValueError):
+            logger.warning(
+                f"ApiClient : could not parse emission timestamp {timestamp!r}, "
+                + "using current time."
+            )
+    return get_datetime_with_timezone()
+
+
 class ApiClient:  # (AsyncClient)
     """
     This class call the Code Carbon API
@@ -190,7 +208,7 @@ def add_emission(self, carbon_emission: dict):
             )
             return False
         emission = EmissionCreate(
-            timestamp=get_datetime_with_timezone(),
+            timestamp=get_measurement_timestamp(carbon_emission.get("timestamp")),
             run_id=self.run_id,
             duration=int(carbon_emission["duration"]),
             emissions_sum=carbon_emission["emissions"],
diff --git a/codecarbon/emissions_tracker.py b/codecarbon/emissions_tracker.py
index 96ed00c91..5b3eec529 100644
--- a/codecarbon/emissions_tracker.py
+++ b/codecarbon/emissions_tracker.py
@@ -1044,6 +1044,9 @@ def _prepare_emissions_data(self) -> EmissionsData:
         )
 
         total_emissions = EmissionsData(
+            # Naive local time. Consumers that need an offset-aware value
+            # (the API client) may assume the local zone -- `.astimezone()` --
+            # precisely because this is `datetime.now()`.
             timestamp=datetime.now().strftime("%Y-%m-%dT%H:%M:%S"),
             project_name=self._project_name,
             run_id=str(self.run_id),
diff --git a/tests/test_api_call.py b/tests/test_api_call.py
index d3b5bd96f..fa813d322 100644
--- a/tests/test_api_call.py
+++ b/tests/test_api_call.py
@@ -1,5 +1,6 @@
 import dataclasses
 import unittest
+from datetime import datetime
 from uuid import uuid4
 
 import requests
@@ -228,6 +229,40 @@ def test_add_emission_skips_short_duration(self):
             )
         )
 
+    def test_add_emission_keeps_measurement_timestamp(self):
+        payload = {
+            "duration": 2,
+            "emissions": 1.0,
+            "emissions_rate": 1.0,
+            "cpu_power": 1.0,
+            "gpu_power": 0.0,
+            "ram_power": 0.5,
+            "cpu_energy": 0.1,
+            "gpu_energy": 0.0,
+            "ram_energy": 0.1,
+            "energy_consumed": 0.2,
+        }
+        with requests_mock.Mocker() as m:
+            m.post("http://test.com/emissions", text="ok", status_code=201)
+            api = ApiClient(
+                endpoint_url="http://test.com",
+                experiment_id="exp-1",
+                conf=conf,
+                create_run_automatically=False,
+            )
+            api.run_id = "run-1"
+
+            # The measurement timestamp is kept, not the time of the POST.
+            api.add_emission({**payload, "timestamp": "2020-01-01T00:00:00"})
+            sent = m.last_request.json()["timestamp"]
+            self.assertTrue(sent.startswith("2020-01-01T00:00:00"))
+            self.assertIsNotNone(datetime.fromisoformat(sent).tzinfo)
+
+            # No timestamp in the payload : fall back to now.
+            api.add_emission(payload)
+            sent = m.last_request.json()["timestamp"]
+            self.assertIsNotNone(datetime.fromisoformat(sent).tzinfo)
+
     def test_add_emission_raises_on_unsuccessful_post(self):
         with requests_mock.Mocker() as m:
             m.post("http://test.com/emissions", text="bad", status_code=500)