diff --git a/io/bits/statx-generic.h b/io/bits/statx-generic.h
index 5859856068..30a24765dc 100644
--- a/io/bits/statx-generic.h
+++ b/io/bits/statx-generic.h
@@ -42,6 +42,7 @@
 # define STATX_BTIME 0x0800U
 # define STATX_MNT_ID 0x1000U
 # define STATX_DIOALIGN 0x2000U
+# define STATX_MNT_ID_UNIQUE 0x4000U
 # define STATX__RESERVED 0x80000000U
 
 # define STATX_ATTR_COMPRESSED 0x0004