diff --git a/sources/machinarium/ds/vrb.c b/sources/machinarium/ds/vrb.c
index 0b0c98f1..d63b024c 100644
--- a/sources/machinarium/ds/vrb.c
+++ b/sources/machinarium/ds/vrb.c
@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/sources/machinarium/write.c b/sources/machinarium/write.c
index 27ce6ed2..11b6b9a5 100644
--- a/sources/machinarium/write.c
+++ b/sources/machinarium/write.c
@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 
 /*
  * machinarium.
