diff --git a/libc/include/byteswap.h b/libc/include/byteswap.h
index 628fb7f..0838e6c 100644
--- a/libc/include/byteswap.h
+++ b/libc/include/byteswap.h
@@ -25,9 +25,11 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+
 #ifndef _BYTESWAP_H_
 #define _BYTESWAP_H_
 
+#include <sys/cdefs.h>
 #include <sys/endian.h>
 
 #define bswap_16(x) __swap16(x)