diff --git a/man2/lseek.2 b/man2/lseek.2
index e10eb4a70..4d7b671be 100644
--- a/man2/lseek.2
+++ b/man2/lseek.2
@@ -44,7 +44,7 @@
 .\" Modified 2003-08-21 by Andries Brouwer <aeb@cwi.nl>
 .\" 2011-09-18, mtk, Added SEEK_DATA + SEEK_HOLE
 .\"
-.TH LSEEK 2 2011-09-25 "Linux" "Linux Programmer's Manual"
+.TH LSEEK 2 2013-03-27 "Linux" "Linux Programmer's Manual"
 .SH NAME
 lseek \- reposition read/write file offset
 .SH SYNOPSIS
@@ -150,6 +150,15 @@ it can be considered to consist of data that is a sequence of zeros).
 .\" https://lkml.org/lkml/2011/4/22/79
 .\" http://lwn.net/Articles/440255/
 .\" http://blogs.oracle.com/bonwick/entry/seek_hole_and_seek_data
+
+The
+.BR _GNU_SOURCE
+feature test macro must be defined in order to obtain the definitions of
+.BR SEEK_DATA
+and
+.BR SEEK_HOLE
+from
+.IR <unistd.h> .
 .SH RETURN VALUE
 Upon successful completion,
 .BR lseek ()