diff --git a/chat/locales/en-US/xmpp.properties b/chat/locales/en-US/xmpp.properties
index 76d649b4f5..5cd285df59 100644
--- a/chat/locales/en-US/xmpp.properties
+++ b/chat/locales/en-US/xmpp.properties
@@ -54,6 +54,7 @@ conversation.error.creationFailedNotAllowed=Access restricted: You are not allow
 #   is not found.
 #   %S is the name of MUC room.
 conversation.error.joinFailedRemoteServerNotFound=Could not join the room %S as the server the room is hosted on could not be reached.
+conversation.error.changeTopicFailedNotAuthorized=You are not authorized to set the topic of this room.
 #   This is displayed in a conversation as an error message when the user sends
 #   a message to a room that he is not in.
 #   %1$S is the name of MUC room.
@@ -127,3 +128,4 @@ odnoklassniki.usernameHint=Profile ID
 #  These are the help messages for each command.
 command.join=join [<room@server>][/<nick>] [<password>]: Join a room, optionally providing a different nickname, or the room password.
 command.part=part [<message>]: Leave the current room with an optional message.
+command.topic=%S [<new topic>]: Set this room's topic.
diff --git a/chat/protocols/xmpp/xmpp-commands.jsm b/chat/protocols/xmpp/xmpp-commands.jsm
index 05606b9c0c..2467d34359 100644
--- a/chat/protocols/xmpp/xmpp-commands.jsm
+++ b/chat/protocols/xmpp/xmpp-commands.jsm
@@ -62,5 +62,16 @@ var commands = [
         conv.part(aMsg);
       return true;
     }
+  },
+  {
+    name: "topic",
+    get helpString() _("command.topic", "topic"),
+    usageContext: Ci.imICommand.CMD_CONTEXT_CHAT,
+    run: function(aMsg, aConv) {
+      let conv = getConv(aConv);
+      if (!conv.left)
+        conv.topic = aMsg;
+      return true;
+    }
   }
 ];
diff --git a/chat/protocols/xmpp/xmpp.jsm b/chat/protocols/xmpp/xmpp.jsm
index e81f2dfe96..b42e9c3f31 100644
--- a/chat/protocols/xmpp/xmpp.jsm
+++ b/chat/protocols/xmpp/xmpp.jsm
@@ -106,6 +106,25 @@ const XMPPMUCConversationPrototype = {
 
   _targetResource: "",
 
+  get topic() this._topic,
+  set topic(aTopic) {
+    let notAuthorized = (aError) => {
+      // XEP-0045 (8.1): Unauthorized subject change.
+      let message = _("conversation.error.changeTopicFailedNotAuthorized");
+      this.writeMessage(this.name, message, {system: true, error: true});
+      return true;
+    };
+    let errorHandler = this._account.handleErrors({forbidden: notAuthorized,
+                                                   notAcceptable: notAuthorized,
+                                                   itemNotFound: notAuthorized});
+
+    // XEP-0045 (8.1): Modifying the room subject.
+    let subject = Stanza.node("subject", null, null, aTopic.trim());
+    let s = Stanza.message(this.name, null, null,{type: "groupchat"}, subject);
+    this._account.sendStanza(s, errorHandler);
+  },
+  get topicSettable() true,
+
   /* Called when the user enters a chat message */
   sendMsg: function (aMsg) {
     let notInRoom = (aError) => {
@@ -228,6 +247,8 @@ const XMPPMUCConversationPrototype = {
       // XEP-0045: Room exists and joined successfully.
       this.left = false;
       this.joining = false;
+      // TODO (Bug 1172350): Implement Service Discovery Extensions (XEP-0128) to obtain
+      // configuration of this room.
     }
 
     if (!this._participants.get(nick)) {
@@ -1218,7 +1239,8 @@ const XMPPAccountPrototype = {
 
   /* Called when a message stanza is received */
   onMessageStanza: function(aStanza) {
-    let norm = this.normalize(aStanza.attributes["from"]);
+    let from = aStanza.attributes["from"];
+    let norm = this.normalize(from);
 
     let type = aStanza.attributes["type"];
     let body;
@@ -1236,6 +1258,22 @@ const XMPPAccountPrototype = {
         body = TXTToHTML(b.innerText);
       }
     }
+
+    let subject = aStanza.getElement(["subject"]);
+    if (subject) {
+      // XEP-0045 (7.2.16): Check for a subject element in the stanza and update
+      // the topic if it exists.
+      // We are breaking the spec because only a message that contains a
+      // <subject/> but no <body/> element shall be considered a subject change
+      // for MUC, but we ignore that to be compatible with ejabberd versions
+      // before 15.06.
+      let muc = this._mucs.get(norm);
+      let nick = this._parseJID(from).resource;
+      // TODO There can be multiple subject elements with different xml:lang
+      // attributes.
+      muc.setTopic(subject.innerText, nick);
+    }
+
     if (body) {
       let date;
       let delay = aStanza.getElement(["delay"]);
@@ -1252,15 +1290,6 @@ const XMPPAccountPrototype = {
           return;
         }
         let muc = this._mucs.get(norm);
-
-        // Check for a subject element in the stanza and update the topic if
-        // it exists.
-        let s = aStanza.getElement(["subject"]);
-        // TODO There can be multiple subject elements with different xml:lang
-        // attributes.
-        if (s)
-          muc.setTopic(s.innerText);
-
         muc.incomingMessage(body, aStanza, date);
         return;
       }