diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index c43efd1..441efdf 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -41,7 +41,7 @@ jobs:
         run: |
           echo ttf-mscorefonts-installer msttcorefonts/accepted-mscorefonts-eula select true | sudo debconf-set-selections
           sudo apt-get update
-          sudo apt-get install xsltproc fop xmlstarlet ttf-mscorefonts-installer graphviz
+          sudo apt-get install xsltproc fop xmlstarlet ttf-mscorefonts-installer graphviz libxml2-utils
           sudo fc-cache -f
       - name: Make XML, HTML and PDF
         run: make html pdf
diff --git a/.github/workflows/pr.yml b/.github/workflows/pr.yml
index 3c6d775..3233e19 100644
--- a/.github/workflows/pr.yml
+++ b/.github/workflows/pr.yml
@@ -39,7 +39,7 @@ jobs:
         run: |
           echo ttf-mscorefonts-installer msttcorefonts/accepted-mscorefonts-eula select true | sudo debconf-set-selections
           sudo apt-get update
-          sudo apt-get install xsltproc fop xmlstarlet ttf-mscorefonts-installer graphviz
+          sudo apt-get install xsltproc fop xmlstarlet ttf-mscorefonts-installer graphviz libxml2-utils
           sudo fc-cache -f
       - name: Make XML, HTML and PDF
         run: make html pdf
diff --git a/dmlex-v1.0/specification/Makefile b/dmlex-v1.0/specification/Makefile
index 1a388fa..a1bc197 100644
--- a/dmlex-v1.0/specification/Makefile
+++ b/dmlex-v1.0/specification/Makefile
@@ -17,6 +17,7 @@ dmlex-$(VERSION).html: dmlex-$(VERSION).xml
 
 dmlex-$(VERSION).xml: dmlex.xml docbook/dbgenent.mod dmlex_uml.svg $(SOURCE_XML)
 	./merge.sh $@
+	xmllint --valid --noout $@
 
 dmlex_uml.pdf: dmlex.dot
 	dot -Tpdf < $< > $@
@@ -44,6 +45,9 @@ xmldep:
 jsondep:
 	@python -c 'import jsonschema' 2>/dev/null || { echo "Python jsonschema module is not installed, cannot validate JSON examples."; exit 2; }
 
+rdfdep:
+	@python -c 'import pyshacl' 2>/dev/null || { echo "Python pyshacl module is not installed, cannot validate JSON examples."; exit 2; }
+
 validate_xml: xmldep validate_xml.py schemas/XML/dmlex.xsd schemas/XML/dmlex_no-crosslingual.xsd
 	@for xmlexample in examples/examples/source/*[0-9].xml; do \
 		echo validating "$$xmlexample"; \
@@ -70,7 +74,7 @@ validate_json: jsondep validate_json.py schemas/JSON/dmlex.schema.json schemas/J
 		   } \
 	done
 
-validate_rdf: jsondep schemas/RDF/dmlex.shacl
+validate_rdf: rdfdep schemas/RDF/dmlex.shacl
 	@for rdfexample in examples/examples/source/*[0-9].rdf; do \
 		echo validating "$$rdfexample"; \
 		python -m pyshacl -s schemas/RDF/dmlex.shacl -df turtle $$rdfexample -e schemas/RDF/dmlex.ttl -i rdfs \