diff --git a/src/main/java/envoy/server/data/Contact.java b/src/main/java/envoy/server/data/Contact.java
index eea8fe1..b629c37 100644
--- a/src/main/java/envoy/server/data/Contact.java
+++ b/src/main/java/envoy/server/data/Contact.java
@@ -35,6 +35,16 @@ public abstract class Contact {
 	 */
 	public abstract envoy.data.Contact toCommon();
 
+	/**
+	 * Transforms this contact into a {@link envoy.data.Contact} where the contacts
+	 * set of contacts is empty.
+	 *
+	 * @return a {@link envoy.data.Contact} object of this contact
+	 *         object.
+	 * @since Envoy Server Standalone v0.1-beta
+	 */
+	protected abstract envoy.data.Contact toFlatCommon();
+
 	/**
 	 * @return the ID of this contact.
 	 * @since Envoy Server Standalone v0.1-beta
diff --git a/src/main/java/envoy/server/data/Group.java b/src/main/java/envoy/server/data/Group.java
index 6301624..595b252 100644
--- a/src/main/java/envoy/server/data/Group.java
+++ b/src/main/java/envoy/server/data/Group.java
@@ -6,8 +6,6 @@ import javax.persistence.Entity;
 import javax.persistence.NamedQuery;
 import javax.persistence.Table;
 
-import envoy.data.User;
-
 /**
  * This class serves as a way to let Hibernate communicate with the server
  * without bringing the dependency of JPA/Hibernate into the client.<br>
@@ -31,6 +29,12 @@ public class Group extends Contact {
 	 */
 	@Override
 	public envoy.data.Group toCommon() {
-		return new envoy.data.Group(id, name, contacts.parallelStream().map(Contact::toCommon).map(User.class::cast).collect(Collectors.toSet()));
+		return new envoy.data.Group(id, name, contacts.parallelStream().map(User.class::cast).map(User::toFlatCommon).collect(Collectors.toSet()));
 	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	@Override
+	protected envoy.data.Group toFlatCommon() { return toCommon(); }
 }
diff --git a/src/main/java/envoy/server/data/User.java b/src/main/java/envoy/server/data/User.java
index fa6db47..3fb167f 100755
--- a/src/main/java/envoy/server/data/User.java
+++ b/src/main/java/envoy/server/data/User.java
@@ -1,6 +1,7 @@
 package envoy.server.data;
 
 import java.util.Date;
+import java.util.Set;
 import java.util.stream.Collectors;
 
 import javax.persistence.*;
@@ -45,9 +46,15 @@ public class User extends Contact {
 	 */
 	@Override
 	public envoy.data.User toCommon() {
-		return new envoy.data.User(id, name, status, contacts.stream().map(Contact::toCommon).collect(Collectors.toSet()));
+		return new envoy.data.User(id, name, status, contacts.parallelStream().map(Contact::toFlatCommon).collect(Collectors.toSet()));
 	}
 
+	/**
+	 * {@inheritDoc}
+	 */
+	@Override
+	protected envoy.data.User toFlatCommon() { return new envoy.data.User(id, name, status, Set.of()); }
+
 	/**
 	 * @return the password hash
 	 * @since Envoy Server Standalone v0.1-alpha