diff --git a/buildbot_nix/__init__.py b/buildbot_nix/__init__.py
index f2eb9e6..1d49d7e 100644
--- a/buildbot_nix/__init__.py
+++ b/buildbot_nix/__init__.py
@@ -105,7 +105,7 @@ class GerritConfig:
         """
         Returns the prefix to build a repourl using that gerrit configuration.
         """
-        return 'ssh://{self.username}@{self.domain}:{self.port}/'
+        return f'ssh://{self.username}@{self.domain}:{self.port}/'
 
 class BuildTrigger(steps.BuildStep):
     def __init__(