diff --git a/libc/kernel/uapi/linux/mman.h b/libc/kernel/uapi/linux/mman.h
index e469374..9cb8776 100644
--- a/libc/kernel/uapi/linux/mman.h
+++ b/libc/kernel/uapi/linux/mman.h
@@ -22,6 +22,7 @@
 #include <asm-generic/hugetlb_encode.h>
 #define MREMAP_MAYMOVE 1
 #define MREMAP_FIXED 2
+#define MREMAP_DONTUNMAP 4
 #define OVERCOMMIT_GUESS 0
 #define OVERCOMMIT_ALWAYS 1
 #define OVERCOMMIT_NEVER 2