diff --git a/docs/tutorial/LangImpl2.html b/docs/tutorial/LangImpl2.html
index 018d0be..3021560 100644
--- a/docs/tutorial/LangImpl2.html
+++ b/docs/tutorial/LangImpl2.html
@@ -815,6 +815,7 @@
 <div class="doc_code">
 <pre>
 #include &lt;cstdio&gt;
+#include &lt;cstdlib&gt;
 #include &lt;string&gt;
 #include &lt;map&gt;
 #include &lt;vector&gt;