diff --git a/libc/kernel/uapi/linux/userfaultfd.h b/libc/kernel/uapi/linux/userfaultfd.h
index e6b776a..fc100ae 100644
--- a/libc/kernel/uapi/linux/userfaultfd.h
+++ b/libc/kernel/uapi/linux/userfaultfd.h
@@ -124,4 +124,5 @@
 #define UFFDIO_WRITEPROTECT_MODE_DONTWAKE ((__u64) 1 << 1)
   __u64 mode;
 };
+#define UFFD_USER_MODE_ONLY 1
 #endif