diff --git a/libc/sysv/consts.sh b/libc/sysv/consts.sh
index 47cdd9b00..5d84f3089 100755
--- a/libc/sysv/consts.sh
+++ b/libc/sysv/consts.sh
@@ -266,6 +266,7 @@ syscon	madv	MADV_HUGEPAGE				14			14			127			127			127			127			127			127			# TOD
 syscon	madv	MADV_NOHUGEPAGE				15			15			127			127			127			127			127			127			# TODO(jart): why would we need it?
 syscon	madv	MADV_DODUMP				17			17			127			127			127			127			127			127			# TODO(jart): what is it?
 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_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_KEEPONFORK.S b/libc/sysv/consts/MADV_KEEPONFORK.S
new file mode 100644
index 000000000..eed8fe329
--- /dev/null
+++ b/libc/sysv/consts/MADV_KEEPONFORK.S
@@ -0,0 +1,2 @@
+#include "libc/sysv/consts/syscon.internal.h"
+.syscon madv,MADV_KEEPONFORK,19,19,127,127,127,127,127,127
diff --git a/libc/sysv/consts/madv.h b/libc/sysv/consts/madv.h
index 90266929b..2b3653805 100644
--- a/libc/sysv/consts/madv.h
+++ b/libc/sysv/consts/madv.h
@@ -21,6 +21,7 @@ extern const unsigned MADV_UNMERGEABLE;
 extern const unsigned MADV_WILLNEED;
 extern const unsigned MADV_SOFT_OFFLINE;
 extern const unsigned MADV_WIPEONFORK;
+extern const unsigned MADV_KEEPONFORK;
 
 #define MADV_NORMAL     0
 #define MADV_RANDOM     1