diff --git a/src/helpers.h b/src/helpers.h
index 602c658..8ba35cb 100644
--- a/src/helpers.h
+++ b/src/helpers.h
@@ -25,6 +25,8 @@
 #ifndef HELPERS_H
 #define HELPERS_H
 
+#include <sys/cdefs.h>
+
 #if (defined(__linux__) || defined(__CYGWIN__)) && !defined(_BE_POSIX)
 # define _GNU_SOURCE
 #elif defined(__sun)