diff --git a/libc/include/features.h b/libc/include/features.h
index 16bea8b2..bc5f8a37 100644
--- a/libc/include/features.h
+++ b/libc/include/features.h
@@ -87,6 +87,8 @@
 	#define __POSIX_OBSOLETE 200112L
 #endif
 
+#define __pure2 __attribute__((__const__))
+
 /* Don't provide things from standard headers that is not implemented. */
 /*#define __SORTIX_SHOW_UNIMPLEMENTED*/