diff --git a/src/libstore/local-overlay-store.hh b/src/libstore/local-overlay-store.hh
index a26392523..66a43d84a 100644
--- a/src/libstore/local-overlay-store.hh
+++ b/src/libstore/local-overlay-store.hh
@@ -128,7 +128,7 @@ private:
 
     void remountIfNecessary();
 
-    bool _remountRequired = false;
+    std::atomic_bool _remountRequired = false;
 };
 
 }