diff --git a/pitfall/pitfall/document.rkt b/pitfall/pitfall/document.rkt
index ef2ef097..dd480d5d 100644
--- a/pitfall/pitfall/document.rkt
+++ b/pitfall/pitfall/document.rkt
@@ -1,4 +1,4 @@
-#lang at-exp racket/base
+#lang debug at-exp racket/base
 (require
   "helper.rkt"
   "param.rkt"
diff --git a/pitfall/pitfall/page.rkt b/pitfall/pitfall/page.rkt
index 39a96ea6..eddb3b7c 100644
--- a/pitfall/pitfall/page.rkt
+++ b/pitfall/pitfall/page.rkt
@@ -1,4 +1,4 @@
-#lang racket/base
+#lang debug racket/base
 (require
   racket/class
   racket/contract
diff --git a/pitfall/pitfall/reference.rkt b/pitfall/pitfall/reference.rkt
index 8a902eb1..4b1e70b9 100644
--- a/pitfall/pitfall/reference.rkt
+++ b/pitfall/pitfall/reference.rkt
@@ -1,4 +1,4 @@
-#lang racket/base
+#lang debug racket/base
 (require
   "helper.rkt"
   "param.rkt"