diff --git a/playwright/_impl/_js_handle.py b/playwright/_impl/_js_handle.py
index 01625ec3f..5a930f1e6 100644
--- a/playwright/_impl/_js_handle.py
+++ b/playwright/_impl/_js_handle.py
@@ -129,7 +129,7 @@ def serialize_value(
         if math.isnan(value):
             return dict(v="NaN")
     if isinstance(value, datetime):
-        return dict(d=value.isoformat())
+        return dict(d=value.isoformat() + "Z")
     if isinstance(value, bool):
         return {"b": value}
     if isinstance(value, (int, float)):
diff --git a/tests/sync/test_assertions.py b/tests/sync/test_assertions.py
index d7180fc94..f2df44ab5 100644
--- a/tests/sync/test_assertions.py
+++ b/tests/sync/test_assertions.py
@@ -12,8 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import datetime
 import re
+from datetime import datetime
 
 import pytest
 
@@ -163,11 +163,7 @@ def test_assertions_locator_to_have_js_property(page: Page, server: Server) -> N
     )
     expect(page.locator("div")).to_have_js_property(
         "foo",
-        {
-            "a": 1,
-            "b": "string",
-            "c": datetime.datetime.fromtimestamp(1627503992000 / 1000),
-        },
+        {"a": 1, "b": "string", "c": datetime.utcfromtimestamp(1627503992000 / 1000)},
     )