Index: src/mate-screensaver-preferences.c
--- src/mate-screensaver-preferences.c.orig
+++ src/mate-screensaver-preferences.c
@@ -1346,7 +1346,7 @@ setup_for_root_user (void)
 }
 
 /* copied from gs-window-x11.c */
-#ifndef _GNU_SOURCE
+#if !defined(_GNU_SOURCE) || defined(__OpenBSD__)
 extern char **environ;
 #endif
 
