diff --git a/changelog.d/9520.misc b/changelog.d/9520.misc
new file mode 100644
index 0000000000..825ba5bbc1
--- /dev/null
+++ b/changelog.d/9520.misc
@@ -0,0 +1 @@
+Add type hints to purge room and server notice admin API.
\ No newline at end of file
diff --git a/synapse/rest/admin/purge_room_servlet.py b/synapse/rest/admin/purge_room_servlet.py
index 8b7bb6d44e..49966ee3e0 100644
--- a/synapse/rest/admin/purge_room_servlet.py
+++ b/synapse/rest/admin/purge_room_servlet.py
@@ -12,13 +12,20 @@
 # 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 typing import TYPE_CHECKING, Tuple
+
 from synapse.http.servlet import (
     RestServlet,
     assert_params_in_dict,
     parse_json_object_from_request,
 )
+from synapse.http.site import SynapseRequest
 from synapse.rest.admin import assert_requester_is_admin
 from synapse.rest.admin._base import admin_patterns
+from synapse.types import JsonDict
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
 
 
 class PurgeRoomServlet(RestServlet):
@@ -36,16 +43,12 @@ class PurgeRoomServlet(RestServlet):
 
     PATTERNS = admin_patterns("/purge_room$")
 
-    def __init__(self, hs):
-        """
-        Args:
-            hs (synapse.server.HomeServer): server
-        """
+    def __init__(self, hs: "HomeServer"):
         self.hs = hs
         self.auth = hs.get_auth()
         self.pagination_handler = hs.get_pagination_handler()
 
-    async def on_POST(self, request):
+    async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         await assert_requester_is_admin(self.auth, request)
 
         body = parse_json_object_from_request(request)
diff --git a/synapse/rest/admin/server_notice_servlet.py b/synapse/rest/admin/server_notice_servlet.py
index 375d055445..f495666f4a 100644
--- a/synapse/rest/admin/server_notice_servlet.py
+++ b/synapse/rest/admin/server_notice_servlet.py
@@ -12,17 +12,24 @@
 # 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 typing import TYPE_CHECKING, Optional, Tuple
+
 from synapse.api.constants import EventTypes
 from synapse.api.errors import SynapseError
+from synapse.http.server import HttpServer
 from synapse.http.servlet import (
     RestServlet,
     assert_params_in_dict,
     parse_json_object_from_request,
 )
+from synapse.http.site import SynapseRequest
 from synapse.rest.admin import assert_requester_is_admin
 from synapse.rest.admin._base import admin_patterns
 from synapse.rest.client.transactions import HttpTransactionCache
-from synapse.types import UserID
+from synapse.types import JsonDict, UserID
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
 
 
 class SendServerNoticeServlet(RestServlet):
@@ -44,17 +51,13 @@ class SendServerNoticeServlet(RestServlet):
     }
     """
 
-    def __init__(self, hs):
-        """
-        Args:
-            hs (synapse.server.HomeServer): server
-        """
+    def __init__(self, hs: "HomeServer"):
         self.hs = hs
         self.auth = hs.get_auth()
         self.txns = HttpTransactionCache(hs)
         self.snm = hs.get_server_notices_manager()
 
-    def register(self, json_resource):
+    def register(self, json_resource: HttpServer):
         PATTERN = "/send_server_notice"
         json_resource.register_paths(
             "POST", admin_patterns(PATTERN + "$"), self.on_POST, self.__class__.__name__
@@ -66,7 +69,9 @@ class SendServerNoticeServlet(RestServlet):
             self.__class__.__name__,
         )
 
-    async def on_POST(self, request, txn_id=None):
+    async def on_POST(
+        self, request: SynapseRequest, txn_id: Optional[str] = None
+    ) -> Tuple[int, JsonDict]:
         await assert_requester_is_admin(self.auth, request)
         body = parse_json_object_from_request(request)
         assert_params_in_dict(body, ("user_id", "content"))
@@ -90,7 +95,7 @@ class SendServerNoticeServlet(RestServlet):
 
         return 200, {"event_id": event.event_id}
 
-    def on_PUT(self, request, txn_id):
+    def on_PUT(self, request: SynapseRequest, txn_id: str) -> Tuple[int, JsonDict]:
         return self.txns.fetch_or_execute_request(
             request, self.on_POST, request, txn_id
         )