diff --git a/dtls_debug.c b/dtls_debug.c
index 28fd0d7f..9c9a0770 100644
--- a/dtls_debug.c
+++ b/dtls_debug.c
@@ -17,6 +17,10 @@
 
 #include "tinydtls.h"
 
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif /* _GNU_SOURCE */
+
 #if defined(HAVE_ASSERT_H) && !defined(assert)
 #include <assert.h>
 #endif