diff --git a/gtk/fnmatch.c b/gtk/fnmatch.c
index 0a45770a40..04eced312f 100644
--- a/gtk/fnmatch.c
+++ b/gtk/fnmatch.c
@@ -20,6 +20,9 @@ Cambridge, MA 02139, USA.  */
 #endif
 
 #include <errno.h>
+/* Added for GTK. We need to make sure that all constants are defined
+ * to properly compile this file */
+#define _GNU_SOURCE
 #include "fnmatch.h"
 #include <ctype.h>