diff --git a/SdmxDataParser/src/main/java/org/sdmxsource/sdmx/dataparser/engine/writer/streaming/StreamCompactDataWriterEngine.java b/SdmxDataParser/src/main/java/org/sdmxsource/sdmx/dataparser/engine/writer/streaming/StreamCompactDataWriterEngine.java
index eeb6438..3bf5b8d 100644
--- a/SdmxDataParser/src/main/java/org/sdmxsource/sdmx/dataparser/engine/writer/streaming/StreamCompactDataWriterEngine.java
+++ b/SdmxDataParser/src/main/java/org/sdmxsource/sdmx/dataparser/engine/writer/streaming/StreamCompactDataWriterEngine.java
@@ -128,6 +128,7 @@ public void startGroup(String groupId, AnnotationBean... annotations) {
 
             if (isTwoPointOne()) {
                 writer.writeStartElement("Group");      //WRITE THE START GROUP
+                writer.writeAttribute(XSI_NS, "type", COMPACT_NS.namespacePrefix + ":" + groupId);
                 writeAnnotations(writer, annotations);
             } else {
                 groupAnnotations = annotations;