diff --git a/src/handlers.rs b/src/handlers.rs
index 3deff3c..d7b07fa 100644
--- a/src/handlers.rs
+++ b/src/handlers.rs
@@ -28,7 +28,7 @@ use xmpp_parsers::{
     message::Message,
     muc::Muc,
     ns,
-    presence::Presence,
+    presence::{Presence, Type as PresenceType},
     stanza_error::{DefinedCondition, ErrorType, StanzaError},
     BareJid, Element, Jid,
 };
@@ -128,7 +128,24 @@ async fn handle_presence<C: ComponentTrait>(
         // Room already exists
         if let Some(room) = rooms.get_mut(&roomjid) {
             debug!("Presence received to existing room: {}", &roomjid);
-            room.add_session(component, realjid, nick).await.unwrap();
+            match room.add_session(component, realjid.clone(), nick).await {
+                Ok(_) => (),
+                Err(Error::NickAlreadyAssigned(nick)) => {
+                    let error = Presence::new(PresenceType::Error)
+                        .with_from(participant)
+                        .with_to(realjid)
+                        .with_payloads(vec![
+                            StanzaError::new(
+                                ErrorType::Cancel,
+                                DefinedCondition::Conflict,
+                                "en",
+                                format!("Nickname conflict: {}", nick),
+                            ).into()
+                        ]);
+                    component.send_stanza(error).await?;
+                },
+                err => err.unwrap(),
+            }
         } else {
             debug!("Presence received to new room: {}", &roomjid);
             let mut room = Room::new(roomjid.clone());
diff --git a/src/room.rs b/src/room.rs
index ecc6517..84b00ce 100644
--- a/src/room.rs
+++ b/src/room.rs
@@ -83,7 +83,7 @@ impl Room {
             // Add into occupants
             let _ = self
                 .occupants
-                .insert(bare.clone(), Occupant::new(realjid.clone()));
+                .insert(bare.clone(), Occupant::new(realjid.clone(), nick.clone()));
 
             // Self-presence
             debug!("Sending self-presence for {}", realjid);
@@ -125,10 +125,10 @@ pub struct Occupant {
 }
 
 impl Occupant {
-    fn new(fulljid: FullJid) -> Occupant {
+    fn new(fulljid: FullJid, nick: Nick) -> Occupant {
         Occupant {
             jid: BareJid::from(fulljid.clone()),
-            nick: fulljid.resource.clone(),
+            nick,
             sessions: vec![fulljid],
         }
     }
@@ -166,7 +166,7 @@ mod tests {
     #[test]
     fn occupant_ignore_dup_session() {
         let fulljid = FullJid::from_str("foo@bar/meh").unwrap();
-        let mut occupant = Occupant::new(fulljid.clone());
+        let mut occupant = Occupant::new(fulljid.clone(), String::from("nick"));
         occupant.add_session(fulljid.clone()).unwrap();
         assert_eq!(occupant.iter().count(), 1);
     }
diff --git a/src/tests.rs b/src/tests.rs
index e558afd..f549615 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -146,3 +146,58 @@ async fn test_0045_join_presence_empty_room() {
         None => panic!(),
     }
 }
+
+#[tokio::test]
+async fn test_0045_join_presence_nick_already_assigned() {
+    let nick = "nick";
+
+    let realjid1 = FullJid::from_str("foo@bar/qxx").unwrap();
+    let realjid2 = FullJid::from_str("qxx@bar/foo").unwrap();
+    let participant = COMPONENT_JID
+        .clone()
+        .with_node("room")
+        .with_resource(nick.clone());
+    let roomjid = COMPONENT_JID.clone().with_node("room");
+
+    // <x xmlns='http://jabber.org/protocol/muc'/>
+    let join1: Element = Presence::new(PresenceType::None)
+        .with_from(Jid::Full(realjid1.clone()))
+        .with_to(Jid::Full(participant.clone()))
+        .with_payloads(vec![Muc::new().into()])
+        .into();
+
+    let join2: Element = Presence::new(PresenceType::None)
+        .with_from(Jid::Full(realjid2.clone()))
+        .with_to(Jid::Full(participant.clone())) // Same participant JID
+        .with_payloads(vec![Muc::new().into()])
+        .into();
+
+    let mut component = TestComponent::new(vec![join1, join2]);
+    let mut rooms: HashMap<BareJid, Room> = HashMap::new();
+
+    // Ignore self-presence for first participant
+    component.expect_with(|_| ());
+    // Ignore message subject for first participant
+    component.expect_with(|_| ());
+
+    component.expect(
+        Presence::new(PresenceType::Error)
+            .with_from(participant)
+            .with_to(realjid2)
+            .with_payloads(vec![StanzaError::new(
+                ErrorType::Cancel,
+                DefinedCondition::Conflict,
+                "en",
+                format!("Nickname conflict: {}", nick),
+            )
+            .into()]),
+    );
+
+    handle_stanza(&mut component, &mut rooms).await.unwrap();
+    component.assert();
+
+    match rooms.get(&roomjid) {
+        Some(_) => (),
+        None => panic!(),
+    }
+}