diff --git a/app/apps/common/oauth_views.py b/app/apps/common/oauth_views.py
index 54733580..a73b3b84 100644
--- a/app/apps/common/oauth_views.py
+++ b/app/apps/common/oauth_views.py
@@ -88,7 +88,7 @@ def _dcr_initial_access_token_ok(request):
     scheme, _, value = header.partition(" ")
     if scheme.lower() != "bearer" or not value:
         return False
-    return hmac.compare_digest(value, expected)
+    return hmac.compare_digest(value.encode(), expected.encode())
 
 
 @require_http_methods(["GET"])
diff --git a/app/apps/common/tests/test_oauth.py b/app/apps/common/tests/test_oauth.py
index b096ada9..7453c923 100644
--- a/app/apps/common/tests/test_oauth.py
+++ b/app/apps/common/tests/test_oauth.py
@@ -224,6 +224,18 @@ class DynamicClientRegistrationInitialAccessTokenTests(TestCase):
         self.assertEqual(response.json()["error"], "invalid_token")
         self.assertEqual(Application.objects.count(), 0)
 
+    def test_rejects_registration_with_non_ascii_initial_access_token(self):
+        response = self.client.post(
+            reverse("oauth-dynamic-client-registration"),
+            data=json.dumps({"redirect_uris": ["http://127.0.0.1:8765/callback"]}),
+            content_type="application/json",
+            HTTP_AUTHORIZATION="Bearer s3cret-iat\u00e9",
+        )
+
+        self.assertEqual(response.status_code, 401)
+        self.assertEqual(response.json()["error"], "invalid_token")
+        self.assertEqual(Application.objects.count(), 0)
+
     def test_allows_registration_with_initial_access_token(self):
         response = self.client.post(
             reverse("oauth-dynamic-client-registration"),