diff -ruN libdvdread-0.9.7-orig/configure libdvdread-0.9.7/configure
--- libdvdread-0.9.7-orig/configure	2006-10-06 03:14:24.000000000 -0500
+++ libdvdread-0.9.7/configure	2023-09-26 21:15:15.000000000 -0500
@@ -3483,6 +3483,7 @@
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 #include <ctype.h>
+#include <stdlib.h>
 #if ((' ' & 0x0FF) == 0x020)
 # define ISLOWER(c) ('a' <= (c) && (c) <= 'z')
 # define TOUPPER(c) (ISLOWER(c) ? 'A' + ((c) - 'a') : (c))