diff --git a/src/docbkx/manual.xml b/src/docbkx/manual.xml
index d6fa1b67..b2e5f403 100644
--- a/src/docbkx/manual.xml
+++ b/src/docbkx/manual.xml
@@ -1,6 +1,6 @@
 <!DOCTYPE book
   PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
-  "http://www.docbook.org/xml/4.2/docbookx.dtd"
+  "https://docbook.org/xml/4.2/docbookx.dtd"
 [
     <!-- "http://www.docbook.org/xml/4.2/docbookx.dtd" -->
     <!-- "file:/sw/share/xml/dtd/docbookx/4.2.0/docbookx.dtd" -->