diff --git a/test/iob.c b/test/iob.c
index 7c4c5ea..a7fb733 100644
--- a/test/iob.c
+++ b/test/iob.c
@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include <assert.h>
 #include <libowfat/iob.h>
 #include <unistd.h>