diff --git a/changelog.d/461.misc b/changelog.d/461.misc
new file mode 100644
index 0000000..e4b16d6
--- /dev/null
+++ b/changelog.d/461.misc
@@ -0,0 +1,1 @@
+Fix a bug introduced in Sydent 2.5.0 where calls to `/_matrix/identity/api/v1/validate/email/requestToken` would fail with an HTTP 500 Internal Server Error if arguments were given as a query string or as a www-form-urlencoded body.
\ No newline at end of file
diff --git a/sydent/http/servlets/__init__.py b/sydent/http/servlets/__init__.py
index 3d8b1e2..de758cf 100644
--- a/sydent/http/servlets/__init__.py
+++ b/sydent/http/servlets/__init__.py
@@ -49,9 +49,13 @@ def get_args(
     Helper function to get arguments for an HTTP request.
     Currently takes args from the top level keys of a json object or
     www-form-urlencoded for backwards compatibility on v1 endpoints only.
-    Returns a tuple (error, args) where if error is non-null,
-    the request is malformed. Otherwise, args contains the
-    parameters passed.
+
+    ⚠️ BEWARE ⚠. If a v1 request provides its args in urlencoded form (either in
+    a POST body or as URL query parameters), then we'll return `Dict[str, str]`.
+    The caller may need to interpret these strings as e.g. an `int`, `bool`, etc.
+    Arguments given as a json body are processed with `json.JSONDecoder.decode`,
+    and so are automatically deserialised to a Python type. The caller should
+    still validate that these have the correct type!
 
     :param request: The request received by the servlet.
     :param args: The args to look for in the request's parameters.
@@ -60,6 +64,10 @@ def get_args(
 
     :raises: MatrixRestError if required is True and a given parameter
         was not found in the request's query parameters.
+    :raises: MatrixRestError if we the request body contains bad JSON.
+    :raises: MatrixRestError if arguments are given in www-form-urlencodedquery
+        form, and some argument name or value is not a valid UTF-8-encoded
+        string.
 
     :return: A dict containing the requested args and their values. String values
         are of type unicode.
diff --git a/sydent/http/servlets/emailservlet.py b/sydent/http/servlets/emailservlet.py
index 11ac04c..d23ed96 100644
--- a/sydent/http/servlets/emailservlet.py
+++ b/sydent/http/servlets/emailservlet.py
@@ -50,9 +50,29 @@ class EmailRequestCodeServlet(Resource):
         args = get_args(request, ("email", "client_secret", "send_attempt"))
 
         email = args["email"]
-        sendAttempt = args["send_attempt"]
         clientSecret = args["client_secret"]
 
+        try:
+            # if we got this via the v1 API in a querystring or urlencoded body,
+            # then the values in args will be a string. So check that
+            # send_attempt is an int.
+            #
+            # NB: We don't check if we're processing a url-encoded v1 request.
+            # This means we accept string representations of integers for
+            # `send_attempt` in v2 requests, and in v1 requests that supply a
+            # JSON body. This is contrary to the spec and leaves me with a dirty
+            # feeling I can't quite shake off.
+            #
+            # Where's Raymond Hettinger when you need him? (THUMP) There must be
+            # a better way!
+            sendAttempt = int(args["send_attempt"])
+        except (TypeError, ValueError):
+            request.setResponseCode(400)
+            return {
+                "errcode": "M_INVALID_PARAM",
+                "error": f"send_attempt should be an integer (got {args['send_attempt']}",
+            }
+
         if not is_valid_client_secret(clientSecret):
             request.setResponseCode(400)
             return {

diff --git a/tests/test_email.py b/tests/test_email.py
index 1420fc2..b7f48c1 100644
--- a/tests/test_email.py
+++ b/tests/test_email.py
@@ -48,7 +48,7 @@ class TestRequestCode(unittest.TestCase):
         request, channel = make_request(
             self.sydent.reactor,
             "POST",
-            "/_matrix/identity/v1/validate/email/requestToken",
+            "/_matrix/identity/api/v1/validate/email/requestToken",
             {
                 "email": "test@test",
                 "client_secret": "oursecret",
@@ -62,13 +62,29 @@ class TestRequestCode(unittest.TestCase):
         email_contents = smtp.sendmail.call_args[0][2].decode("utf-8")
         self.assertIn("Confirm your email address for Matrix", email_contents)
 
+    def test_request_code_via_url_query_params(self):
+        self.sydent.run()
+        url = (
+            "/_matrix/identity/api/v1/validate/email/requestToken?"
+            "email=test@test"
+            "&client_secret=oursecret"
+            "&send_attempt=0"
+        )
+        request, channel = make_request(self.sydent.reactor, "POST", url)
+        smtp = self._render_request(request)
+        self.assertEqual(channel.code, 200)
+
+        # Ensure the email is as expected.
+        email_contents = smtp.sendmail.call_args[0][2].decode("utf-8")
+        self.assertIn("Confirm your email address for Matrix", email_contents)
+
     def test_branded_request_code(self):
         self.sydent.run()
 
         request, channel = make_request(
             self.sydent.reactor,
             "POST",
-            "/_matrix/identity/v1/validate/email/requestToken?brand=vector-im",
+            "/_matrix/identity/api/v1/validate/email/requestToken?brand=vector-im",
             {
                 "email": "test@test",
                 "client_secret": "oursecret",

Email validator incorrectly handling `sendAttempt`
Introduced in 57ba780bbd27fdffbb6fdf6c4044393f35cb4e16

The annotation for `sendAttempt` is incorrect. It is a `str`. Mypy cannot spot this because it is fed something of type `Any` GRRRRRR.

https://sentry.matrix.org/sentry/sydent/issues/234999/?query=is%3Aunresolved
tests/test_email.py::TestRequestCode::test_request_code_via_url_query_params
tests/test_email.py::TestRequestCode::test_branded_request_code tests/test_email.py::TestRequestCode::test_request_code