diff --git a/Makefile b/Makefile
index 54d3dcc..7977779 100644
--- a/Makefile
+++ b/Makefile
@@ -81,7 +81,7 @@ pve-admin-guide.html: ${PVE_ADMIN_GUIDE_SOURCES}
 
 pve-admin-guide.pdf: ${PVE_ADMIN_GUIDE_SOURCES} docinfo.xml pve-admin-guide-docinfo.xml
 	grep ">Release ${RELEASE}<" pve-admin-guide-docinfo.xml || (echo "wrong release in  pve-admin-guide-docinfo.xml" && false);
-	a2x -a docinfo -a docinfo1 -f pdf -L --dblatex-opts "-P latex.output.revhistory=0" pve-admin-guide.adoc
+	a2x -a docinfo -a docinfo1 -f pdf -L --dblatex-opts "-P latex.output.revhistory=0" --dblatex-opts "-P latex.class.options=12pt" pve-admin-guide.adoc
 	test -z "$${NOVIEW}" && $(BROWSER) $@ &
 
 pve-admin-guide.epub: ${PVE_ADMIN_GUIDE_SOURCES}