diff -ruN gerbv-2.6.0-orig/src/interface.c gerbv-2.6.0/src/interface.c
--- gerbv-2.6.0-orig/src/interface.c	2011-12-24 21:41:23.000000000 -0600
+++ gerbv-2.6.0/src/interface.c	2021-10-05 06:54:00.000000000 -0500
@@ -35,6 +35,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <math.h>
 
 #include <gdk/gdkkeysyms.h>