diff --git a/libc/include/sys/sendfile.h b/libc/include/sys/sendfile.h
index c588e68..f90498a 100644
--- a/libc/include/sys/sendfile.h
+++ b/libc/include/sys/sendfile.h
@@ -35,11 +35,12 @@
 __BEGIN_DECLS
 
 #if defined(__USE_FILE_OFFSET64)
-extern ssize_t sendfile(int out_fd, int in_fd, off_t* offset, size_t count) __RENAME(sendfile64);
+extern ssize_t sendfile(int out_fd, int in_fd, off_t* offset, size_t count) __RENAME(sendfile64)
+  __INTRODUCED_IN(21);
 #else
 extern ssize_t sendfile(int out_fd, int in_fd, off_t* offset, size_t count);
 #endif
-extern ssize_t sendfile64(int out_fd, int in_fd, off64_t* offset, size_t count);
+extern ssize_t sendfile64(int out_fd, int in_fd, off64_t* offset, size_t count) __INTRODUCED_IN(21);
 
 __END_DECLS