diff --git a/doc/manual/Makefile.am b/doc/manual/Makefile.am
index b313f112..c9cd932d 100644
--- a/doc/manual/Makefile.am
+++ b/doc/manual/Makefile.am
@@ -1,6 +1,6 @@
 DOCBOOK_FILES = installation.xml introduction.xml manual.xml projects.xml
 
-EXTRA_DIST = $(DOCBOOK_FILES) manual.pdf
+EXTRA_DIST = $(DOCBOOK_FILES)
 
 xsltproc_opts =					\
  --param html.stylesheet \'style.css\'		\
@@ -16,7 +16,7 @@ dist_html_DATA = manual.html style.css
 dist_pdf_DATA = manual.pdf
 
 # Embed Docbook's callout images in the distribution.
-EXTRA_DIST = images
+EXTRA_DIST += images
 
 manual.html: $(DOCBOOK_FILES)
 	if test "$(XSLTPROC)" != ""; then				\