--- 3rdparty/gl2ps/gl2ps.c.orig	2012-01-29 18:15:34.000000000 -0500
+++ 3rdparty/gl2ps/gl2ps.c	2012-01-29 18:16:08.000000000 -0500
@@ -47,6 +47,7 @@
 #endif
 
 #if defined(GL2PS_HAVE_LIBPNG)
+#include <zlib.h>
 #include <png.h>
 #endif