diff --git a/src/clapper/rc.py b/src/clapper/rc.py
index f709038167dbb3b457df38def00eb0126c73b728..dfbd7c466103e77ae2deeb657b1097a4bc2f16bc 100644
--- a/src/clapper/rc.py
+++ b/src/clapper/rc.py
@@ -156,7 +156,7 @@ class UserDefaults(collections.abc.MutableMapping):
                 if not isinstance(base, dict):
                     raise KeyError(
                         f"You are trying to set configuration key "
-                        f"{k}, but {'.'.join(parts[:(n+1)])} is already a "
+                        f"{k}, but {'.'.join(parts[:(n + 1)])} is already a "
                         f"variable set in the file, and not a section"
                     )
             base[parts[-1]] = v