See https://gitlab.com/agmartin/linuxdoc-tools/issues/4
and https://gitlab.com/agmartin/linuxdoc-tools/issues/6

diff --git a/Makefile.in b/Makefile.in
index adb85d0..f215678 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -83,13 +83,14 @@ ifneq ($(BUILDDOC_FORMATS),)
 #    -- Build documentation
 	@echo "Building documentation ..."
 	(cd doc; \
+		MAKE="$(MAKE)" \
 		PREFIX=$(prefix) \
 		BUILD_ISO_ENTITIES=$(BUILD_ISO_ENTITIES) \
 		BUILD_ENTITY_MAP=$(BUILD_ENTITY_MAP) \
-	 	PKGPERL5LIB=$(CURDIR)/perl5lib \
-	 	PKGDATADIR=$(CURDIR)/lib \
+		PKGPERL5LIB=$(CURDIR)/perl5lib \
+		PKGDATADIR=$(CURDIR)/lib \
 		PKGENTITYMAPDIR=$(CURDIR)/entity-map \
-	 	BUILDDOC_FORMATS="$(BUILDDOC_FORMATS)" \
+		BUILDDOC_FORMATS="$(BUILDDOC_FORMATS)" \
 		sh Makedoc.sh)
 endif
 
@@ -174,7 +175,7 @@ ifneq ($(BUILDDOC_FORMATS),)
 	mkdir -m 755 -p $(doc_ddir)
 	# cp -r doc/* $(doc_ddir)
 	( cd doc && tar --exclude='CVS' -cpf - . ) | ( cd $(doc_ddir) && tar -xpf - )
-	rm -f $(doc_ddir)/Makedoc.sh
+	rm -f $(doc_ddir)/Makedoc.sh $(doc_ddir)/Makefile
 	find $(doc_ddir) -type d -print | xargs chmod 755
 	find $(doc_ddir) -type f -print | xargs chmod 644
 endif
diff --git a/doc/Makedoc.sh b/doc/Makedoc.sh
index b7e2efb..da4be99 100644
--- a/doc/Makedoc.sh
+++ b/doc/Makedoc.sh
@@ -33,7 +33,7 @@ if [ "${BUILD_ENTITY_MAP}" = "true" ]; then
     # Create a modified EntityMap.pm with entity-map location in doc
     # build temporary dir. Need to properly install entity-map there.
     mkdir $TMPDIR/Text
-    make -C ../entity-map install DESTDIR="$TMPDIR"
+    ${MAKE} -C ../entity-map install DESTDIR="$TMPDIR"
     sed < ../entity-map/EntityMap.pm.in > $TMPDIR/Text/EntityMap.pm \
 	-e 's|\@localentitymapdir\@|'${TMPDIR}'/usr/share/entity-map|g' \
 	-e 's|\@entitymapdir\@|'${TMPDIR}'/usr/share/entity-map/0.1.0|g'
@@ -49,7 +49,7 @@ fi
 if [ "${BUILD_ISO_ENTITIES}" = "true" ]; then
     # --without-installed-iso-entities: Install iso-entities in
     # "$TMPDIR/usr" and set it as iso-entities prefix.
-    make -C ../iso-entities install DESTDIR="$TMPDIR"
+    ${MAKE} -C ../iso-entities install DESTDIR="$TMPDIR"
     ISOENTITIES_PREFIX="${TMPDIR}/usr"
 else
     # --with-installed-iso-entities: Use system prefix.
@@ -88,45 +88,42 @@ fi
 
 # Build actual documentation
 echo "- Building documentation for formats: ${BUILDDOC_FORMATS}" >&2
+BUILDDOC_MAKE=""
 for docformat in ${BUILDDOC_FORMATS}; do
     case ${docformat} in
 	txt)
-	    echo "- Building txt docs" >&2
 	    if [ -n "`which groff`" ]; then
-		$TMPDIR/linuxdoc --backend=txt --filter --blanks=1 ./guide.sgml
+		echo "- Add to build list: guide.txt" >&2
+		BUILDDOC_MAKE="${BUILDDOC_MAKE} guide.txt"
 	    else
 		echo "- ++ Warning: groff not available, cannot build \"${docformat}\" format." >&2
 	    fi
 	    ;;
 	pdf)
-	    echo "- Building pdf docs" >&2
-	    $TMPDIR/linuxdoc --backend=latex --output=pdf \
-			     --pass="\usepackage{times}" ./guide.sgml
+	    echo "- Add to build list: guide.pdf" >&2
+	    BUILDDOC_MAKE="${BUILDDOC_MAKE} guide.pdf"
 	    ;;
 	info)
-	    echo "- Building info docs" >&2
-	    $TMPDIR/linuxdoc --backend=info ./guide.sgml
+	    echo "- Add to build list: guide.info" >&2
+	    BUILDDOC_MAKE="${BUILDDOC_MAKE} guide.info"
 	    ;;
 	lyx)
-	    echo "- Building lyx docs" >&2
-	    $TMPDIR/linuxdoc --backend=lyx ./guide.sgml
+	    echo "- Add to build list: guide.lyx" >&2
+	    BUILDDOC_MAKE="${BUILDDOC_MAKE} guide.lyx"
 	    ;;
 	html)
-	    echo "- Building html docs" >&2
-	    $TMPDIR/linuxdoc --imagebuttons --backend=html ./guide.sgml \
-		&& mv -f ./guide*.html ./html
+	    echo "- Add to build list: guide.html" >&2
+	    BUILDDOC_MAKE="${BUILDDOC_MAKE} html/guide.html"
 	    ;;
 	rtf)
-	    echo "- Building rtf docs" >&2
-	    $TMPDIR/linuxdoc --backend=rtf ./guide.sgml && if [ ! -d ./rtf ]; \
-		then mkdir -m 755 ./rtf; fi && mv -f ./guide*.rtf ./rtf
+	    echo "- Add to build list: guide.rtf" >&2
+	    BUILDDOC_MAKE="${BUILDDOC_MAKE} rtf/guide.rtf"
 	    ;;
 	dvi+ps)
 	    echo "- Building latex docs" >&2
 	    if [ -n "`which latex`" ]; then
-		echo "- Building dvi docs" >&2
-		$TMPDIR/linuxdoc --backend=latex --output=dvi \
-				 --pass="\usepackage{times}" ./guide.sgml
+		echo "- Add to build list: guide.dvi" >&2
+		BUILDDOC_MAKE="${BUILDDOC_MAKE} guide.dvi"
 
 		if [ -n "`which dvips`" ]; then
 		    echo "   + dvips" >&2
@@ -137,9 +134,13 @@ for docformat in ${BUILDDOC_FORMATS}; do
 			    DVIPS_PAPER="letter"
 			fi
 		    fi
-		    dvips -t ${DVIPS_PAPER} -o ./guide.ps ./guide.dvi
-		    if [ -n "`which gzip`" -a -f ./guide.ps ]; then
-			gzip -fn ./guide.ps
+
+		    if [ -n "`which gzip`" ]; then
+			echo "- Add to build list: guide.ps.gz" >&2
+			BUILDDOC_MAKE="${BUILDDOC_MAKE} guide.ps.gz"
+		    else
+			echo "- Add to build list: guide.ps" >&2
+			BUILDDOC_MAKE="${BUILDDOC_MAKE} guide.ps"
 		    fi
 		else
 		    echo "- ++ Warning: dvips not available, cannot build \"guide.ps\"." >&2
@@ -156,7 +157,9 @@ for docformat in ${BUILDDOC_FORMATS}; do
     esac
 done
 
+${MAKE} TMPDIR="${TMPDIR}" DVIPS_PAPER="${DVIPS_PAPER}" ${BUILDDOC_MAKE}
+
 # Remove temporary directory.
-rm -rf $TMPDIR
+rm -rf "${TMPDIR}"
 
 exit 0
diff --git a/doc/Makefile b/doc/Makefile
new file mode 100644
index 0000000..79c5382
--- /dev/null
+++ b/doc/Makefile
@@ -0,0 +1,44 @@
+
+
+%.txt: %.sgml
+	@echo "- Building txt docs" >&2
+	$(TMPDIR)/linuxdoc --backend=txt --filter --blanks=1 $<
+
+%.pdf: %.sgml
+	@echo "- Building pdf docs" >&2
+	$(TMPDIR)/linuxdoc --backend=latex \
+			--output=pdf \
+			--pass="\usepackage{times}" $<
+
+%.info: %.sgml
+	@echo "- Building info docs" >&2
+	$(TMPDIR)/linuxdoc --backend=info $<
+
+%.lyx: %.sgml
+	@echo "- Building lyx docs" >&2
+	$(TMPDIR)/linuxdoc --backend=lyx $<
+
+html/%.html: %.sgml
+	@echo "- Building html docs" >&2
+	$(TMPDIR)/linuxdoc --imagebuttons --backend=html $<
+	mv -f ./guide*.html ./html
+
+rtf/%.rtf: %.sgml
+	@echo "- Building rtf docs" >&2
+	$(TMPDIR)/linuxdoc --backend=rtf $<
+	mkdir -m 755 -p ./rtf
+	mv -f ./guide*.rtf ./rtf
+
+%.dvi: %.sgml
+	@echo "- Building dvi docs" >&2
+	$(TMPDIR)/linuxdoc --backend=latex \
+			--output=dvi \
+			--pass="\usepackage{times}" $<
+
+%.ps: %.dvi
+	@echo "- Building ps docs" >&2
+	dvips -t $(DVIPS_PAPER) -o $@ $<
+
+%.ps.gz: %.ps
+	@echo "- Building ps.gz docs" >&2
+	gzip -fn $<