diff --git a/jena-sparql-api-sparql-ext/src/main/java/org/aksw/jena_sparql_api/sparql/ext/xml/RDFDatatypeXml.java b/jena-sparql-api-sparql-ext/src/main/java/org/aksw/jena_sparql_api/sparql/ext/xml/RDFDatatypeXml.java
index eb3ed2ca1..23b86eaae 100644
--- a/jena-sparql-api-sparql-ext/src/main/java/org/aksw/jena_sparql_api/sparql/ext/xml/RDFDatatypeXml.java
+++ b/jena-sparql-api-sparql-ext/src/main/java/org/aksw/jena_sparql_api/sparql/ext/xml/RDFDatatypeXml.java
@@ -96,7 +96,7 @@ public String unparse(Object value) {
      * @throws DatatypeFormatException if the lexical form is not legal
      */
     @Override
-    public Node parse(String lexicalForm) throws DatatypeFormatException {
+    public synchronized Node parse(String lexicalForm) throws DatatypeFormatException {
         Document result;
 		try {
 			result = documentBuilder.parse(new InputSource(new StringReader(lexicalForm)));