diff --git a/libc/kernel/uapi/asm-generic/mman-common.h b/libc/kernel/uapi/asm-generic/mman-common.h
index e96f4cc..966d05b 100644
--- a/libc/kernel/uapi/asm-generic/mman-common.h
+++ b/libc/kernel/uapi/asm-generic/mman-common.h
@@ -63,6 +63,7 @@
 #define MADV_POPULATE_READ 22
 #define MADV_POPULATE_WRITE 23
 #define MADV_DONTNEED_LOCKED 24
+#define MADV_COLLAPSE 25
 #define MAP_FILE 0
 #define PKEY_DISABLE_ACCESS 0x1
 #define PKEY_DISABLE_WRITE 0x2