diff --git a/doc/manual/Makefile.am b/doc/manual/Makefile.am
index 65f1f3f441..5bd256658b 100644
--- a/doc/manual/Makefile.am
+++ b/doc/manual/Makefile.am
@@ -1,13 +1,12 @@
 DOCBOOK_DTD = /nix/current/xml/dtd/docbook
 DOCBOOK_XSL = /nix/current/xml/xsl/docbook
-XML = /usr/share/doc/packages/sp/html-xml/xml.soc
 
 SOURCES = book.xml introduction.xml installation.xml nix-reference.xml \
  troubleshooting.xml bugs.xml
 
 book.is-valid: $(SOURCES)
-	SP_CHARSET_FIXED=YES SP_ENCODING=XML \
-	nsgmls -wxml -c $(XML) -c $(DOCBOOK_DTD)/docbook.cat -ges $<
+	SGML_CATALOG_FILES=$(DOCBOOK_DTD)/docbook.cat \
+	xmllint --catalogs --noout --valid book.xml
 	touch $@
 
 man1_MANS = nix.1 fix.1
diff --git a/doc/manual/book.xml b/doc/manual/book.xml
index 1f54d4efda..a2035fca7f 100644
--- a/doc/manual/book.xml
+++ b/doc/manual/book.xml
@@ -1,5 +1,7 @@
 <?xml version="1.0"?>
-<!DOCTYPE book SYSTEM "/nix/current/xml/dtd/docbook/docbookx.dtd"
+<!DOCTYPE book
+    PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+    "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
 [
 <!ENTITY introduction SYSTEM "introduction.xml">
 <!ENTITY installation SYSTEM "installation.xml">