diff --git a/zerver/lib/actions.py b/zerver/lib/actions.py
index 8c2315ab07..cfcd93767f 100644
--- a/zerver/lib/actions.py
+++ b/zerver/lib/actions.py
@@ -2238,8 +2238,6 @@ def check_send_typing_notification(sender: UserProfile, user_ids: List[int], ope
     realm = sender.realm
     if len(user_ids) == 0:
         raise JsonableError(_("Missing parameter: 'to' (recipient)"))
-    elif operator not in ("start", "stop"):
-        raise JsonableError(_("Invalid 'op' value (should be start or stop)"))
 
     """ The next chunk of code will go away when we upgrade old mobile
     users away from versions of mobile that send emails.  For the
diff --git a/zerver/tests/test_typing.py b/zerver/tests/test_typing.py
index 3ed9d6be76..da20b73803 100644
--- a/zerver/tests/test_typing.py
+++ b/zerver/tests/test_typing.py
@@ -29,7 +29,7 @@ class TypingValidateOperatorTest(ZulipTestCase):
             op="foo",
         )
         result = self.api_post(sender, "/api/v1/typing", params)
-        self.assert_json_error(result, "Invalid 'op' value (should be start or stop)")
+        self.assert_json_error(result, "Invalid op")
 
 
 class TypingValidateUsersTest(ZulipTestCase):
diff --git a/zerver/views/typing.py b/zerver/views/typing.py
index d1eb691234..de0af3d34a 100644
--- a/zerver/views/typing.py
+++ b/zerver/views/typing.py
@@ -5,15 +5,17 @@ from django.http import HttpRequest, HttpResponse
 from zerver.decorator import REQ, has_request_variables
 from zerver.lib.actions import check_send_typing_notification
 from zerver.lib.response import json_success
-from zerver.lib.validator import check_int, check_list
+from zerver.lib.validator import check_int, check_list, check_string_in
 from zerver.models import UserProfile
 
+VALID_OPERATOR_TYPES = ["start", "stop"]
+
 
 @has_request_variables
 def send_notification_backend(
     request: HttpRequest,
     user_profile: UserProfile,
-    operator: str = REQ("op"),
+    operator: str = REQ("op", str_validator=check_string_in(VALID_OPERATOR_TYPES)),
     notification_to: List[int] = REQ("to", validator=check_list(check_int)),
 ) -> HttpResponse:
     check_send_typing_notification(user_profile, notification_to, operator)