diff --git a/find-toplevel-variables.rkt b/find-toplevel-variables.rkt
index 0e146a4..31b3878 100644
--- a/find-toplevel-variables.rkt
+++ b/find-toplevel-variables.rkt
@@ -25,7 +25,8 @@
        (loop (Assign-value exp))]
       
       [(Def? exp)
-       (loop (Def-value exp))]
+       (cons (Def-variable exp)
+             (loop (Def-value exp)))]
       
       [(Branch? exp)
        (append (loop (Branch-predicate exp))