diff --git a/libc/kernel/uapi/linux/bits.h b/libc/kernel/uapi/linux/bits.h
index d747e24..2b8dbe2 100644
--- a/libc/kernel/uapi/linux/bits.h
+++ b/libc/kernel/uapi/linux/bits.h
@@ -8,4 +8,5 @@
 #define _UAPI_LINUX_BITS_H
 #define __GENMASK(h,l) (((~_UL(0)) - (_UL(1) << (l)) + 1) & (~_UL(0) >> (__BITS_PER_LONG - 1 - (h))))
 #define __GENMASK_ULL(h,l) (((~_ULL(0)) - (_ULL(1) << (l)) + 1) & (~_ULL(0) >> (__BITS_PER_LONG_LONG - 1 - (h))))
+#define __GENMASK_U128(h,l) ((_BIT128((h)) << 1) - (_BIT128(l)))
 #endif