diff --git a/libc/sysv/consts.sh b/libc/sysv/consts.sh
index d8b346226..038619359 100755
--- a/libc/sysv/consts.sh
+++ b/libc/sysv/consts.sh
@@ -270,6 +270,7 @@ syscon	madv	MADV_KEEPONFORK				19			19			127			127			127			127			127			127			# T
 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_POPULATE_READ				22			22			127			127			127			127			127			127			# TODO: add support ?
+syscon	madv	MADV_POPULATE_WRITE				23			23			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_POPULATE_WRITE.S b/libc/sysv/consts/MADV_POPULATE_WRITE.S
new file mode 100644
index 000000000..2b0992039
--- /dev/null
+++ b/libc/sysv/consts/MADV_POPULATE_WRITE.S
@@ -0,0 +1,2 @@
+#include "libc/sysv/consts/syscon.internal.h"
+.syscon madv,MADV_POPULATE_WRITE,23,23,127,127,127,127,127,127
diff --git a/libc/sysv/consts/madv.h b/libc/sysv/consts/madv.h
index b70fc831b..5b00895c1 100644
--- a/libc/sysv/consts/madv.h
+++ b/libc/sysv/consts/madv.h
@@ -25,6 +25,7 @@ extern const unsigned MADV_KEEPONFORK;
 extern const unsigned MADV_COLD;
 extern const unsigned MADV_PAGEOUT;
 extern const unsigned MADV_POPULATE_READ;
+extern const unsigned MADV_POPULATE_WRITE;
 
 #define MADV_NORMAL     0
 #define MADV_RANDOM     1