diff --git a/src/main/java/de/thm/arsnova/services/IUserService.java b/src/main/java/de/thm/arsnova/services/IUserService.java
index 1231bf9c117f3ba89c50bc4aaf3ee53fb533a268..b95e1b03e5fa04157fe8fbb8c0a52ff0b461440a 100644
--- a/src/main/java/de/thm/arsnova/services/IUserService.java
+++ b/src/main/java/de/thm/arsnova/services/IUserService.java
@@ -39,7 +39,7 @@ public interface IUserService {
 
 	boolean isUserInSession(User user, String keyword);
 
-	List<User> getUsersInSession(String keyword);
+	Set<User> getUsersInSession(String keyword);
 
 	void addCurrentUserToSessionMap(String keyword);
 
diff --git a/src/main/java/de/thm/arsnova/services/UserService.java b/src/main/java/de/thm/arsnova/services/UserService.java
index 84d952172fd9fd10e2e931e17d7db33716c876fc..8db052e055ce1d1c1e3e6e625cbeeb809f07ff6b 100644
--- a/src/main/java/de/thm/arsnova/services/UserService.java
+++ b/src/main/java/de/thm/arsnova/services/UserService.java
@@ -7,7 +7,7 @@ import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.io.OutputStream;
-import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.Hashtable;
 import java.util.List;
 import java.util.Map;
@@ -148,8 +148,8 @@ public class UserService implements IUserService, InitializingBean, DisposableBe
 	}
 
 	@Override
-	public List<User> getUsersInSession(String keyword) {
-		List<User> result = new ArrayList<User>();
+	public Set<User> getUsersInSession(String keyword) {
+		Set<User> result = new HashSet<User>();
 		for (Entry<User, String> e : user2session.entrySet()) {
 			if (e.getValue().equals(keyword)) {
 				result.add(e.getKey());
diff --git a/src/main/java/de/thm/arsnova/socket/ARSnovaSocketIOServer.java b/src/main/java/de/thm/arsnova/socket/ARSnovaSocketIOServer.java
index be88f17ad179d47b1b8b1936bfa30d56850d4557..224faa86bb56043f70c4ac98e938c95a9fe7496a 100644
--- a/src/main/java/de/thm/arsnova/socket/ARSnovaSocketIOServer.java
+++ b/src/main/java/de/thm/arsnova/socket/ARSnovaSocketIOServer.java
@@ -265,7 +265,7 @@ public class ARSnovaSocketIOServer {
 		 * all connected clients and if send feedback, if user is in current
 		 * session
 		 */
-		List<User> users = userService.getUsersInSession(sessionKey);
+		Set<User> users = userService.getUsersInSession(sessionKey);
 
 		for (SocketIOClient c : server.getAllClients()) {
 			User u = userService.getUser2SocketId(c.getSessionId());