diff --git a/buildbot_nix/__init__.py b/buildbot_nix/__init__.py
index 315af1b..a7f33e8 100644
--- a/buildbot_nix/__init__.py
+++ b/buildbot_nix/__init__.py
@@ -721,7 +721,7 @@ class NixConfigurator(ConfiguratorBase):
                 project.owner,
                 project.repo,
                 self.github.token(),
-                f"{self.url}/change_hook/github",
+                self.url + "change_hook/github",
                 webhook_secret,
             )