diff --git a/tests/functional/local-overlay-store/common.sh b/tests/functional/local-overlay-store/common.sh
index 27338ea23..cbdb3a1f7 100644
--- a/tests/functional/local-overlay-store/common.sh
+++ b/tests/functional/local-overlay-store/common.sh
@@ -69,7 +69,7 @@ mountOverlayfs () {
     || skipTest "overlayfs is not supported"
 
   cleanupOverlay () {
-    umount "$storeBRoot/nix/store"
+    umount -n "$storeBRoot/nix/store"
     rm -r $storeVolume/workdir
   }
   trap cleanupOverlay EXIT