diff --git a/CHANGELOG.md b/CHANGELOG.md
index 03a2243ed..bbbc7484f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -52,6 +52,10 @@ to include examples, links to docs, or any other relevant information.
 
 ### Fixed
 
+- Encoding a datetime search attribute without a timezone now raises
+  `ValueError("Timezone must be present on all search attribute dates")` on
+  the typed path, matching the deprecated untyped encoder, instead of sending
+  a naive ISO string that the server rejects with `BadSearchAttributes`.
 - `GoogleAdkPlugin` now passes the optional `anthropic`, `litellm`, and `openai` SDKs through
   the workflow sandbox.
 - `contrib.deepagents`: prevent duplicate input messages after continue-as-new.
diff --git a/temporalio/converter/_search_attributes.py b/temporalio/converter/_search_attributes.py
index 4ec154d6f..4a8191bbd 100644
--- a/temporalio/converter/_search_attributes.py
+++ b/temporalio/converter/_search_attributes.py
@@ -61,6 +61,8 @@ def encode_typed_search_attribute_value(
         )
     # datetime needs to be in isoformat
     if isinstance(value, datetime):
+        if value.tzinfo is None:
+            raise ValueError("Timezone must be present on all search attribute dates")
         value = value.isoformat()
     # We'll do an extra sanity check for keyword list and check every value
     if isinstance(value, Sequence):
diff --git a/tests/test_converter.py b/tests/test_converter.py
index 4c64e25ba..4d791c342 100644
--- a/tests/test_converter.py
+++ b/tests/test_converter.py
@@ -47,6 +47,7 @@
     create_payload_validation_error,
     decode_search_attributes,
     encode_search_attribute_values,
+    encode_typed_search_attribute_value,
     value_to_type,
 )
 from temporalio.exceptions import (
@@ -285,6 +286,18 @@ def test_encode_search_attribute_values():
         encode_search_attribute_values(["foo", 123])  # type: ignore[arg-type]
 
 
+def test_encode_typed_search_attribute_value_datetime_requires_timezone():
+    key = temporalio.common.SearchAttributeKey.for_datetime("checkout_time")
+    with pytest.raises(ValueError, match="Timezone must be present"):
+        encode_typed_search_attribute_value(
+            key, datetime(2024, 7, 5, 15, 43, 7, 875302)
+        )
+    payload = encode_typed_search_attribute_value(
+        key, datetime(2024, 7, 5, 15, 43, 7, 875302, tzinfo=timezone.utc)
+    )
+    assert payload.metadata["type"] == b"Datetime"
+
+
 def test_decode_search_attributes():
     """Tests decode from protobuf for python types"""