diff --git a/src/libstore/realisation.cc b/src/libstore/realisation.cc
index c9b66186f..e4276c040 100644
--- a/src/libstore/realisation.cc
+++ b/src/libstore/realisation.cc
@@ -65,7 +65,7 @@ void RealisedPath::closure(
     ret.insert(pathsClosure.begin(), pathsClosure.end());
 }
 
-void RealisedPath::closure(Store& store, RealisedPath::Set& ret) const
+void RealisedPath::closure(Store& store, RealisedPath::Set & ret) const
 {
     RealisedPath::closure(store, {*this}, ret);
 }