diff --git a/redex-lib/redex/tut-subst.rkt b/redex-lib/redex/tut-subst.rkt
index 255c623c..5157eff2 100644
--- a/redex-lib/redex/tut-subst.rkt
+++ b/redex-lib/redex/tut-subst.rkt
@@ -97,6 +97,8 @@ for untyped.
     (match body
       [`(λ (,xs ,ts) ... ,body)
        (set-subtract (loop body) (apply set xs))]
+      [`(λ ,(? symbol? xs) ... ,body)
+       (set-subtract (loop body) (apply set xs))]
       [(? x?)
        (set body)]
       [(? list?)