--- a/sct.c	2017-09-22 00:44:20.270421881 +0000
+++ b/sct.c	2017-09-26 10:50:38.964562740 +0000
@@ -36,6 +36,7 @@
 main(int argc, char **argv)
 {
 	Display *dpy = XOpenDisplay(NULL);
+	if (!dpy) exit(1);
 	int screen = DefaultScreen(dpy);
 	Window root = RootWindow(dpy, screen);