diff --git a/overlays.nix b/overlays.nix
index b515e9d..c798667 100644
--- a/overlays.nix
+++ b/overlays.nix
@@ -19,7 +19,7 @@ final: prev: {
 
        MISSING=""
        for target in "$@"; do
-          if ! echo "$MOUNTED" | grep -Fxq "$target"; then
+          if ! grep -Fxq "$target" <<< "$MOUNTED"; then
              MISSING="$MISSING $target"
           fi
        done