diff --git a/doc/ncurses-intro.doc b/doc/ncurses-intro.doc
index 85179d1..1d72f80 100644
--- a/doc/ncurses-intro.doc
+++ b/doc/ncurses-intro.doc
@@ -332,6 +332,7 @@
    function names and parameters as mentioned above.
 
    Here is a sample program to motivate the discussion:
+#include <stdlib.h>
 #include <curses.h>
 #include <signal.h>