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-rw-r--r--include/ouroboros/endian.h5
1 files changed, 4 insertions, 1 deletions
diff --git a/include/ouroboros/endian.h b/include/ouroboros/endian.h
index f29b6749..04c2246a 100644
--- a/include/ouroboros/endian.h
+++ b/include/ouroboros/endian.h
@@ -23,9 +23,12 @@
#ifndef OUROBOROS_ENDIAN_H
#define OUROBOROS_ENDIAN_H
+
#if defined(__linux__) || defined(__CYGWIN__) || \
(defined(__MACH__) && !defined(__APPLE__))
-#define _DEFAULT_SOURCE
+#ifndef _DEFAULT_SOURCE
+#error You must define _DEFAULT_SOURCE before including this file
+#endif
#include <endian.h>
#elif defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__)
#include <sys/endian.h>