diff --git a/purple/purplexpcom/public/purpleIConversation.idl b/purple/purplexpcom/public/purpleIConversation.idl
index 43fc75e1c4..e04e5e91fa 100644
--- a/purple/purplexpcom/public/purpleIConversation.idl
+++ b/purple/purplexpcom/public/purpleIConversation.idl
@@ -122,12 +122,16 @@ interface purpleIConvChat: purpleIConversation {
      The list of people participating in this chat */
   nsISimpleEnumerator getParticipants();
 
-  /* The topic of this chat room  (FIXME settable?) */
-  readonly attribute AUTF8String topic;
+  /* The topic of this chat room */
+           attribute AUTF8String topic;
 
   /* The name/nick of the person who set the topic */
   readonly attribute AUTF8String topicSetter;
 
+  /* Whether the protocol plugin can set a topic. Doesn't check that
+     the user has the necessary rights in the current conversation. */
+  readonly attribute boolean topicSettable;
+
   /* The nick seen by other people in the room */
   readonly attribute AUTF8String nick;
 
diff --git a/purple/purplexpcom/src/imConversations.js b/purple/purplexpcom/src/imConversations.js
index 217839a21e..95b88c447d 100644
--- a/purple/purplexpcom/src/imConversations.js
+++ b/purple/purplexpcom/src/imConversations.js
@@ -270,7 +270,9 @@ UIConversation.prototype = {
   // Chat only
   getParticipants: function() this.target.getParticipants(),
   get topic() this.target.topic,
+  set topic(aTopic) { this.target.topic = aTopic; },
   get topicSetter() this.target.topicSetter,
+  get topicSettable() this.target.topicSettable,
   get nick() this.target.nick,
   get left() this.target.left
 };
diff --git a/purple/purplexpcom/src/jsProtoHelper.jsm b/purple/purplexpcom/src/jsProtoHelper.jsm
index 95435a096d..482fcb74e7 100644
--- a/purple/purplexpcom/src/jsProtoHelper.jsm
+++ b/purple/purplexpcom/src/jsProtoHelper.jsm
@@ -554,6 +554,7 @@ const GenericConvChatPrototype = {
   get nick() this._nick,
   get topic() this._topic,
   get topicSetter() this._topicSetter,
+  get topicSettable() false,
   get left() false,
 
   getParticipants: function() {