diff --git a/datadog_lambda/metric.py b/datadog_lambda/metric.py
index 3bc9955f..44f8e377 100644
--- a/datadog_lambda/metric.py
+++ b/datadog_lambda/metric.py
@@ -65,6 +65,8 @@ def lambda_metric(metric_name, value, timestamp=None, tags=None, force_async=Fal
         timestamp_ceiling = int(
             (datetime.now() - timedelta(hours=4)).timestamp()
         )  # 4 hours ago
+        if isinstance(timestamp, datetime):
+            timestamp = int(timestamp.timestamp())
         if timestamp_ceiling > timestamp:
             logger.warning(
                 "Timestamp %s is older than 4 hours, not submitting metric %s",
diff --git a/tests/test_metric.py b/tests/test_metric.py
index 031b1180..10ef9191 100644
--- a/tests/test_metric.py
+++ b/tests/test_metric.py
@@ -58,6 +58,19 @@ def test_lambda_metric_timestamp_with_extension(self):
             "test_timestamp", 1, timestamp=timestamp, tags=[dd_lambda_layer_tag]
         )
 
+    @patch("datadog_lambda.metric.should_use_extension", True)
+    def test_lambda_metric_datetime_with_extension(self):
+        patcher = patch("datadog_lambda.metric.extension_thread_stats")
+        self.mock_metric_extension_thread_stats = patcher.start()
+        self.addCleanup(patcher.stop)
+
+        delta = timedelta(hours=5)
+        timestamp = datetime.now() - delta
+
+        lambda_metric("test_timestamp", 1, timestamp)
+        self.mock_metric_lambda_stats.distribution.assert_not_called()
+        self.mock_metric_extension_thread_stats.distribution.assert_not_called()
+
     @patch("datadog_lambda.metric.should_use_extension", True)
     def test_lambda_metric_invalid_timestamp_with_extension(self):
         patcher = patch("datadog_lambda.metric.extension_thread_stats")