diff --git a/winsup/doc/ChangeLog b/winsup/doc/ChangeLog
index aefb41e2b..814e65156 100644
--- a/winsup/doc/ChangeLog
+++ b/winsup/doc/ChangeLog
@@ -1,3 +1,7 @@
+2015-03-13  Jon TURNEY  <jon.turney@dronecode.org.uk>
+
+	* Makefile.in (prefix): Define.
+
 2015-03-12  Corinna Vinschen  <corinna@vinschen.de>
 
 	* ntsec.xml (ntsec-mapping-nsswitch-desc): Fix typo.
diff --git a/winsup/doc/Makefile.in b/winsup/doc/Makefile.in
index b7a8dbd8d..8bf86f703 100644
--- a/winsup/doc/Makefile.in
+++ b/winsup/doc/Makefile.in
@@ -12,6 +12,7 @@ SHELL = @SHELL@
 srcdir = @srcdir@
 VPATH = @srcdir@
 
+prefix:=@prefix@
 datarootdir:=@datarootdir@
 docdir = @docdir@
 htmldir = @htmldir@