diff --git a/jupyter_server/services/events/handlers.py b/jupyter_server/services/events/handlers.py
index a345df27b..0357a9f45 100644
--- a/jupyter_server/services/events/handlers.py
+++ b/jupyter_server/services/events/handlers.py
@@ -10,7 +10,6 @@
 from typing import TYPE_CHECKING, Any, Dict, Optional, cast
 
 from jupyter_core.utils import ensure_async
-from jupyter_events.logger import SchemaNotRegistered
 from tornado import web, websocket
 
 from jupyter_server.auth.decorator import authorized, ws_authenticated
@@ -112,21 +111,21 @@ async def post(self):
             raise web.HTTPError(400, "No JSON data provided")
 
         try:
+            # Validate payload and verify schema is registered.
             validate_model(payload)
+            schema_id = cast(str, payload.get("schema_id"))
+            schema = self.event_logger.schemas.get(schema_id)
             self.event_logger.emit(
-                schema_id=cast(str, payload.get("schema_id")),
+                schema_id=schema.id,
                 data=cast("Dict[str, Any]", payload.get("data")),
                 timestamp_override=get_timestamp(payload),
             )
             self.set_status(204)
             self.finish()
-        except web.HTTPError:
-            raise
-        except SchemaNotRegistered as e:
-            message = f"Unregistered event schema: ${str(e)}"
-            raise web.HTTPError(400, message) from e
         except Exception as e:
-            raise web.HTTPError(500, str(e)) from e
+            # All known exceptions are raised by bad requests, e.g.,
+            # unregistered schema, invalid emission data payload, etc.
+            raise web.HTTPError(400, str(e)) from e
 
 
 default_handlers = [
diff --git a/tests/services/events/test_api.py b/tests/services/events/test_api.py
index 019a44e21..6dfebd0ba 100644
--- a/tests/services/events/test_api.py
+++ b/tests/services/events/test_api.py
@@ -127,15 +127,6 @@ async def test_post_event(jp_fetch, event_logger_sink, payload):
 }
 """
 
-
-@pytest.mark.parametrize("payload", [payload_3, payload_4, payload_5, payload_6, payload_7])
-async def test_post_event_400(jp_fetch, event_logger, payload):
-    with pytest.raises(tornado.httpclient.HTTPClientError) as e:
-        await jp_fetch("api", "events", method="POST", body=payload)
-
-    assert expected_http_error(e, 400)
-
-
 payload_8 = """\
 {
     "schema_id": "http://event.mock.jupyter.org/message",
@@ -157,9 +148,14 @@ async def test_post_event_400(jp_fetch, event_logger, payload):
 """
 
 
-@pytest.mark.parametrize("payload", [payload_8, payload_9])
-async def test_post_event_500(jp_fetch, event_logger, payload):
-    with pytest.raises(tornado.httpclient.HTTPClientError) as e:
+@pytest.mark.parametrize(
+    "payload",
+    [payload_3, payload_4, payload_5, payload_6, payload_7, payload_8, payload_9],
+)
+async def test_post_event_400(jp_fetch, event_logger, payload):
+    try:
         await jp_fetch("api", "events", method="POST", body=payload)
-
-    assert expected_http_error(e, 500)
+    except Exception as exception:
+        assert exception.code == 400
+        return
+    assert "failed" == True