diff --git a/validator/src/main/java/org/mustangproject/validator/Validator.java b/validator/src/main/java/org/mustangproject/validator/Validator.java
index 545ee574..c3372126 100644
--- a/validator/src/main/java/org/mustangproject/validator/Validator.java
+++ b/validator/src/main/java/org/mustangproject/validator/Validator.java
@@ -61,6 +61,9 @@ public abstract class Validator {
 		Source xmlData = new StreamSource(new ByteArrayInputStream(xmlRawData));
 		SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
 		try {
+			schemaFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
+			schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");
+			schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
 			Schema schema = schemaFactory.newSchema(schemaFile);
 			javax.xml.validation.Validator validator = schema.newValidator();
 			validator.validate(xmlData);