diff --git a/doc/Makefile.am b/doc/Makefile.am
index df5db7e5..8c29d045 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -55,7 +55,7 @@ html-local: $(MAN_HTML)
 	    -aversion=$(VERSION) $(ASCIIDOC_EXTRA) -o $@ $<
 
 %.html: %.asciidoc
-	$(AM_V_GEN)$(ASCIIDOC) -b html -d article -f asciidoc.conf \
+	$(AM_V_GEN)$(ASCIIDOC) -b html4 -d article -f asciidoc.conf \
 		-aversion=$(VERSION) $(ASCIIDOC_EXTRA) -o $@ $<
 
 doc_DATA = $(MAN_HTML)
diff --git a/doc/Makefile.in b/doc/Makefile.in
index f0ce1a78..da965f8e 100644
--- a/doc/Makefile.in
+++ b/doc/Makefile.in
@@ -620,7 +620,7 @@ html-local: $(MAN_HTML)
 	    -aversion=$(VERSION) $(ASCIIDOC_EXTRA) -o $@ $<
 
 %.html: %.asciidoc
-	$(AM_V_GEN)$(ASCIIDOC) -b html -d article -f asciidoc.conf \
+	$(AM_V_GEN)$(ASCIIDOC) -b html4 -d article -f asciidoc.conf \
 		-aversion=$(VERSION) $(ASCIIDOC_EXTRA) -o $@ $<
 
 # Tell versions [3.59,3.63) of GNU make to not export all variables.