diff --git a/libc/include/sys/sem.h b/libc/include/sys/sem.h
index a1ecd1f..753fc37 100644
--- a/libc/include/sys/sem.h
+++ b/libc/include/sys/sem.h
@@ -29,6 +29,7 @@
 #ifndef _SYS_SEM_H_
 #define _SYS_SEM_H_
 
+#include <sys/cdefs.h>
 #include <linux/sem.h>
 
 #endif /* _SYS_SEM_H_ */