diff --git a/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializer.java b/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializer.java
index a5ae08858..250544068 100644
--- a/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializer.java
+++ b/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializer.java
@@ -139,6 +139,7 @@ public class MetadataDocumentXmlSerializer {
   private static final String ABSTRACT = "Abstract";
 
   private static final String XML_ANNOTATIONS = "Annotations";
+  private static final String OPEN_TYPE = "OpenType";
 
   private static final String EDMX = "Edmx";
   private static final String PREFIX_EDMX = "edmx";
@@ -772,7 +773,11 @@ public class MetadataDocumentXmlSerializer {
       if (complexType.isAbstract()) {
         writer.writeAttribute(ABSTRACT, TRUE);
       }
-
+      
+      if (complexType.isOpenType()) {
+          writer.writeAttribute(OPEN_TYPE, TRUE);
+      }
+      
       appendProperties(writer, complexType);
 
       appendNavigationProperties(writer, complexType);
@@ -801,6 +806,10 @@ public class MetadataDocumentXmlSerializer {
         writer.writeAttribute(ABSTRACT, TRUE);
       }
 
+      if (entityType.isOpenType()) {
+          writer.writeAttribute(OPEN_TYPE, TRUE);
+      }      
+      
       appendKey(writer, entityType);
 
       appendProperties(writer, entityType);
diff --git a/lib/server-core/src/test/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializerTest.java b/lib/server-core/src/test/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializerTest.java
index 449253f72..b6db975a4 100644
--- a/lib/server-core/src/test/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializerTest.java
+++ b/lib/server-core/src/test/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializerTest.java
@@ -450,7 +450,7 @@ public class MetadataDocumentXmlSerializerTest {
 
     InputStream metadataStream = serializer.metadataDocument(serviceMetadata).getContent();
     String metadata = IOUtils.toString(metadataStream);
-    assertTrue(metadata.contains("<ComplexType Name=\"ComplexType\" Abstract=\"true\">"
+    assertTrue(metadata.contains("<ComplexType Name=\"ComplexType\" Abstract=\"true\" OpenType=\"true\">"
         + "<Property Name=\"prop1\" Type=\"Edm.String\"/>"
         + "<Property Name=\"prop2\" Type=\"Edm.String\"/>"
         + "</ComplexType>"));