diff -durN libicns-0.8.1.orig/icnsutils/png2icns.c libicns-0.8.1/icnsutils/png2icns.c
--- libicns-0.8.1.orig/icnsutils/png2icns.c	2012-06-14 01:42:07.000000000 +0200
+++ libicns-0.8.1/icnsutils/png2icns.c	2016-12-04 17:51:16.117504444 +0100
@@ -22,6 +22,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdint.h>
+#include <unistd.h>
 
 #include <errno.h>