diff --git a/changelog.d/14632.bugfix b/changelog.d/14632.bugfix
new file mode 100644
index 000000000..323d10f1b
--- /dev/null
+++ b/changelog.d/14632.bugfix
@@ -0,0 +1 @@
+Reject invalid read receipt requests with empty room or event IDs. Contributed by Nick @ Beeper (@fizzadar).
diff --git a/synapse/rest/client/receipts.py b/synapse/rest/client/receipts.py
index 18a282b22..28b7d30ea 100644
--- a/synapse/rest/client/receipts.py
+++ b/synapse/rest/client/receipts.py
@@ -20,7 +20,7 @@ from synapse.api.errors import Codes, SynapseError
 from synapse.http.server import HttpServer
 from synapse.http.servlet import RestServlet, parse_json_object_from_request
 from synapse.http.site import SynapseRequest
-from synapse.types import JsonDict
+from synapse.types import EventID, JsonDict, RoomID
 
 from ._base import client_patterns
 
@@ -56,6 +56,9 @@ class ReceiptRestServlet(RestServlet):
     ) -> Tuple[int, JsonDict]:
         requester = await self.auth.get_user_by_req(request)
 
+        if not RoomID.is_valid(room_id) or not event_id.startswith(EventID.SIGIL):
+            raise SynapseError(400, "A valid room ID and event ID must be specified")
+
         if receipt_type not in self._known_receipt_types:
             raise SynapseError(
                 400,
diff --git a/tests/rest/client/test_receipts.py b/tests/rest/client/test_receipts.py
new file mode 100644
index 000000000..2a7fcea38
--- /dev/null
+++ b/tests/rest/client/test_receipts.py
@@ -0,0 +1,76 @@
+# Copyright 2022 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from twisted.test.proto_helpers import MemoryReactor
+
+import synapse.rest.admin
+from synapse.rest.client import login, receipts, register
+from synapse.server import HomeServer
+from synapse.util import Clock
+
+from tests import unittest
+
+
+class ReceiptsTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        login.register_servlets,
+        register.register_servlets,
+        receipts.register_servlets,
+        synapse.rest.admin.register_servlets,
+    ]
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.owner = self.register_user("owner", "pass")
+        self.owner_tok = self.login("owner", "pass")
+
+    def test_send_receipt(self) -> None:
+        channel = self.make_request(
+            "POST",
+            "/rooms/!abc:beep/receipt/m.read/$def",
+            content={},
+            access_token=self.owner_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+
+    def test_send_receipt_invalid_room_id(self) -> None:
+        channel = self.make_request(
+            "POST",
+            "/rooms/not-a-room-id/receipt/m.read/$def",
+            content={},
+            access_token=self.owner_tok,
+        )
+        self.assertEqual(channel.code, 400, channel.result)
+        self.assertEqual(
+            channel.json_body["error"], "A valid room ID and event ID must be specified"
+        )
+
+    def test_send_receipt_invalid_event_id(self) -> None:
+        channel = self.make_request(
+            "POST",
+            "/rooms/!abc:beep/receipt/m.read/not-an-event-id",
+            content={},
+            access_token=self.owner_tok,
+        )
+        self.assertEqual(channel.code, 400, channel.result)
+        self.assertEqual(
+            channel.json_body["error"], "A valid room ID and event ID must be specified"
+        )
+
+    def test_send_receipt_invalid_receipt_type(self) -> None:
+        channel = self.make_request(
+            "POST",
+            "/rooms/!abc:beep/receipt/invalid-receipt-type/$def",
+            content={},
+            access_token=self.owner_tok,
+        )
+        self.assertEqual(channel.code, 400, channel.result)