diff --git a/libc/sysv/consts.sh b/libc/sysv/consts.sh
index 522663ea0..256111c8d 100755
--- a/libc/sysv/consts.sh
+++ b/libc/sysv/consts.sh
@@ -268,6 +268,7 @@ syscon	madv	MADV_DODUMP				17			17			127			127			127			127			127			127			# TODO(
 syscon	madv	MADV_WIPEONFORK				18			18			127			127			127			127			127			127			# TODO: add support ?
 syscon	madv	MADV_KEEPONFORK				19			19			127			127			127			127			127			127			# TODO: add support ?
 syscon	madv	MADV_COLD				20			20			127			127			127			127			127			127			# TODO: add support ?
+syscon	madv	MADV_PAGEOUT				21			21			127			127			127			127			127			127			# TODO: add support ?
 syscon	madv	MADV_DOFORK				11			11			127			127			127			127			127			127			# TODO(jart): what is it?
 syscon	madv	MADV_DONTDUMP				16			16			127			127			127			127			127			127			# see MAP_CONCEAL in OpenBSD; TODO(jart): what is it?
 syscon	madv	MADV_DONTFORK				10			10			127			127			127			127			127			127			# TODO(jart): what is it?
diff --git a/libc/sysv/consts/MADV_PAGEOUT.S b/libc/sysv/consts/MADV_PAGEOUT.S
new file mode 100644
index 000000000..a3b0e06ab
--- /dev/null
+++ b/libc/sysv/consts/MADV_PAGEOUT.S
@@ -0,0 +1,2 @@
+#include "libc/sysv/consts/syscon.internal.h"
+.syscon madv,MADV_PAGEOUT,21,21,127,127,127,127,127,127
diff --git a/libc/sysv/consts/madv.h b/libc/sysv/consts/madv.h
index 97c4839b3..a1d083bf4 100644
--- a/libc/sysv/consts/madv.h
+++ b/libc/sysv/consts/madv.h
@@ -23,6 +23,7 @@ extern const unsigned MADV_SOFT_OFFLINE;
 extern const unsigned MADV_WIPEONFORK;
 extern const unsigned MADV_KEEPONFORK;
 extern const unsigned MADV_COLD;
+extern const unsigned MADV_PAGEOUT;
 
 #define MADV_NORMAL     0
 #define MADV_RANDOM     1