diff --git a/beautiful-racket-demo/basic-demo/expander.rkt b/beautiful-racket-demo/basic-demo/expander.rkt
index 82ff395..b676d75 100644
--- a/beautiful-racket-demo/basic-demo/expander.rkt
+++ b/beautiful-racket-demo/basic-demo/expander.rkt
@@ -40,8 +40,9 @@
               (or
                (and (exact-positive-integer? clsv)
                     (vector-member clsv line-vec))
-               (error (format "error in line ~a: line ~a not found"
-                              line-num clsv))))])
+               (error
+                (format "error in line ~a: line ~a not found"
+                        line-num clsv))))])
         (line-func)
         (add1 line-idx)))))