diff -Nurd marco-1.22.0/src/ui/theme.c marco-1.22.0.new/src/ui/theme.c
--- marco-1.22.0/src/ui/theme.c	2019-02-08 08:51:33.000000000 -0600
+++ marco-1.22.0.new/src/ui/theme.c	2019-03-23 06:00:16.139892136 -0500
@@ -60,7 +60,7 @@
 #include <gtk/gtk.h>
 #include <string.h>
 #include <stdlib.h>
-#define __USE_XOPEN
+#define _XOPEN_SOURCE
 #include <math.h>
 
 #define GDK_COLOR_RGBA(color)                                           \