diff --git a/app/assets/javascripts/discourse/controllers/topic-bulk-actions.js.es6 b/app/assets/javascripts/discourse/controllers/topic-bulk-actions.js.es6
index 97dd5accc..144c6f082 100644
--- a/app/assets/javascripts/discourse/controllers/topic-bulk-actions.js.es6
+++ b/app/assets/javascripts/discourse/controllers/topic-bulk-actions.js.es6
@@ -67,10 +67,10 @@ export default Ember.ArrayController.extend(Discourse.ModalFunctionality, {
     },
 
     changeCategory: function() {
-      var category = Discourse.Category.findById(parseInt(this.get('newCategoryId'), 10)),
-          categoryName = (category ? category.get('name') : null),
+      var categoryId = parseInt(this.get('newCategoryId'), 10) || 0,
+          category = Discourse.Category.findById(categoryId),
           self = this;
-      this.perform({type: 'change_category', category_name: categoryName}).then(function(topics) {
+      this.perform({type: 'change_category', category_id: categoryId}).then(function(topics) {
         topics.forEach(function(t) {
           t.set('category', category);
         });
diff --git a/app/assets/javascripts/discourse/controllers/topic_controller.js b/app/assets/javascripts/discourse/controllers/topic_controller.js
index 15f9c1b59..c52c72e46 100644
--- a/app/assets/javascripts/discourse/controllers/topic_controller.js
+++ b/app/assets/javascripts/discourse/controllers/topic_controller.js
@@ -214,7 +214,6 @@ Discourse.TopicController = Discourse.ObjectController.extend(Discourse.Selected
     },
 
     finishedEditingTopic: function() {
-      var topicController = this;
       if (this.get('editingTopic')) {
 
         var topic = this.get('model');
@@ -230,6 +229,7 @@ Discourse.TopicController = Discourse.ObjectController.extend(Discourse.Selected
         });
 
         // save the modifications
+        var self = this;
         topic.save().then(function(result){
           // update the title if it has been changed (cleaned up) server-side
           var title       = result.basic_topic.title;
@@ -238,10 +238,10 @@ Discourse.TopicController = Discourse.ObjectController.extend(Discourse.Selected
             title: title,
             fancy_title: fancy_title
           });
-          topicController.set('topicSaving', false);
+          self.set('topicSaving', false);
         }, function(error) {
-          topicController.set('editingTopic', true);
-          topicController.set('topicSaving', false);
+          self.set('editingTopic', true);
+          self.set('topicSaving', false);
           if (error && error.responseText) {
             bootbox.alert($.parseJSON(error.responseText).errors[0]);
           } else {
@@ -250,7 +250,7 @@ Discourse.TopicController = Discourse.ObjectController.extend(Discourse.Selected
         });
 
         // close editing mode
-        topicController.set('editingTopic', false);
+        self.set('editingTopic', false);
       }
     },
 
diff --git a/app/assets/javascripts/discourse/models/topic.js b/app/assets/javascripts/discourse/models/topic.js
index 7a309f3fe..cb6943d9b 100644
--- a/app/assets/javascripts/discourse/models/topic.js
+++ b/app/assets/javascripts/discourse/models/topic.js
@@ -193,7 +193,7 @@ Discourse.Topic = Discourse.Model.extend({
 
     return Discourse.ajax(this.get('url'), {
       type: 'PUT',
-      data: { title: this.get('title'), category: this.get('category.name') }
+      data: { title: this.get('title'), category_id: this.get('category.id') }
     });
   },
 
diff --git a/app/assets/javascripts/discourse/models/topic_tracking_state.js b/app/assets/javascripts/discourse/models/topic_tracking_state.js
index 29b79e7f4..94d009cfe 100644
--- a/app/assets/javascripts/discourse/models/topic_tracking_state.js
+++ b/app/assets/javascripts/discourse/models/topic_tracking_state.js
@@ -124,7 +124,7 @@ Discourse.TopicTrackingState = Discourse.Model.extend({
 
       row.highest_post_number = topic.highest_post_number;
       if (topic.category) {
-        row.category_name = topic.category.name;
+        row.category_id = topic.category.id;
       }
 
       tracker.states["t" + topic.id] = row;
@@ -137,7 +137,7 @@ Discourse.TopicTrackingState = Discourse.Model.extend({
     this.set("messageCount", this.get("messageCount") + 1);
   },
 
-  countNew: function(category_name){
+  countNew: function(category_id){
     return _.chain(this.states)
       .where({last_read_post_number: null})
       .where(function(topic) {
@@ -145,7 +145,7 @@ Discourse.TopicTrackingState = Discourse.Model.extend({
         return (topic.notification_level !== 0 && !topic.notification_level) ||
                topic.notification_level >= Discourse.Topic.NotificationLevel.TRACKING;
       })
-      .where(function(topic){ return topic.category_name === category_name || !category_name;})
+      .where(function(topic){ return topic.category_id === category_id || !category_id;})
       .value()
       .length;
   },
@@ -159,22 +159,22 @@ Discourse.TopicTrackingState = Discourse.Model.extend({
     });
   },
 
-  countUnread: function(category_name){
+  countUnread: function(category_id){
     return _.chain(this.states)
       .where(function(topic){
         return topic.last_read_post_number !== null &&
                topic.last_read_post_number < topic.highest_post_number;
       })
       .where(function(topic) { return topic.notification_level >= Discourse.Topic.NotificationLevel.TRACKING})
-      .where(function(topic){ return topic.category_name === category_name || !category_name;})
+      .where(function(topic){ return topic.category_id === category_id || !category_id;})
       .value()
       .length;
   },
 
-  countCategory: function(category) {
+  countCategory: function(category_id) {
     var count = 0;
     _.each(this.states, function(topic){
-      if (topic.category_name === category) {
+      if (topic.category_id === category_id) {
         count += (topic.last_read_post_number === null ||
                   topic.last_read_post_number < topic.highest_post_number) ? 1 : 0;
       }
diff --git a/app/controllers/posts_controller.rb b/app/controllers/posts_controller.rb
index 674ebc4cf..1d42fc4b3 100644
--- a/app/controllers/posts_controller.rb
+++ b/app/controllers/posts_controller.rb
@@ -106,11 +106,11 @@ class PostsController < ApplicationController
     # to stay consistent with the create api,
     #  we should allow for title changes and category changes here
     #  we should also move all of this to a post updater.
-    if post.post_number == 1 && (params[:title] || params[:post][:category])
+    if post.post_number == 1 && (params[:title] || params[:post][:category_id])
       post.topic.acting_user = current_user
       post.topic.title = params[:title] if params[:title]
       Topic.transaction do
-        post.topic.change_category(params[:post][:category])
+        post.topic.change_category_to_id(params[:post][:category_id].to_i)
         post.topic.save
       end
 
diff --git a/app/controllers/topics_controller.rb b/app/controllers/topics_controller.rb
index 3328fcf60..0949e9d48 100644
--- a/app/controllers/topics_controller.rb
+++ b/app/controllers/topics_controller.rb
@@ -113,7 +113,7 @@ class TopicsController < ApplicationController
 
     success = false
     Topic.transaction do
-      success = topic.save && topic.change_category(params[:category])
+      success = topic.save && topic.change_category_to_id(params[:category_id].to_i)
     end
 
     # this is used to return the title to the client as it may have been changed by "TextCleaner"
diff --git a/app/models/topic.rb b/app/models/topic.rb
index 87816f92b..71fde80df 100644
--- a/app/models/topic.rb
+++ b/app/models/topic.rb
@@ -493,13 +493,12 @@ class Topic < ActiveRecord::Base
     new_post
   end
 
-  # Changes the category to a new name
-  def change_category(name)
+  def change_category_to_id(category_id)
     # If the category name is blank, reset the attribute
-    if name.blank?
+    if (category_id.nil? || category_id.to_i == 0)
       cat = Category.find_by(id: SiteSetting.uncategorized_category_id)
     else
-      cat = Category.find_by(name: name)
+      cat = Category.where(id: category_id).first
     end
 
     return true if cat == category
@@ -507,7 +506,6 @@ class Topic < ActiveRecord::Base
     changed_to_category(cat)
   end
 
-
   def remove_allowed_user(username)
     user = User.find_by(username: username)
     if user
diff --git a/app/models/topic_tracking_state.rb b/app/models/topic_tracking_state.rb
index 1e1bd25a2..fbc5325ec 100644
--- a/app/models/topic_tracking_state.rb
+++ b/app/models/topic_tracking_state.rb
@@ -14,7 +14,7 @@ class TopicTrackingState
                 :highest_post_number,
                 :last_read_post_number,
                 :created_at,
-                :category_name,
+                :category_id,
                 :notification_level
 
   def self.publish_new(topic)
@@ -118,7 +118,7 @@ class TopicTrackingState
            topics.created_at,
            highest_post_number,
            last_read_post_number,
-           c.name AS category_name,
+           c.id AS category_id,
            tu.notification_level
     FROM users u
     INNER JOIN user_stats AS us ON us.user_id = u.id
diff --git a/app/serializers/topic_tracking_state_serializer.rb b/app/serializers/topic_tracking_state_serializer.rb
index f90e8f646..f023863bf 100644
--- a/app/serializers/topic_tracking_state_serializer.rb
+++ b/app/serializers/topic_tracking_state_serializer.rb
@@ -1,3 +1,8 @@
 class TopicTrackingStateSerializer < ApplicationSerializer
-  attributes :topic_id, :highest_post_number, :last_read_post_number, :created_at, :category_name, :notification_level
+  attributes :topic_id,
+             :highest_post_number,
+             :last_read_post_number,
+             :created_at,
+             :category_id,
+             :notification_level
 end
diff --git a/lib/topics_bulk_action.rb b/lib/topics_bulk_action.rb
index a0ee6f4ad..eb04a2903 100644
--- a/lib/topics_bulk_action.rb
+++ b/lib/topics_bulk_action.rb
@@ -26,7 +26,7 @@ class TopicsBulkAction
     def change_category
       topics.each do |t|
         if guardian.can_edit?(t)
-          @changed_ids << t.id if t.change_category(@operation[:category_name])
+          @changed_ids << t.id if t.change_category_to_id(@operation[:category_id])
         end
       end
     end
diff --git a/spec/components/topics_bulk_action_spec.rb b/spec/components/topics_bulk_action_spec.rb
index 1473677e9..00e56aa3a 100644
--- a/spec/components/topics_bulk_action_spec.rb
+++ b/spec/components/topics_bulk_action_spec.rb
@@ -18,7 +18,7 @@ describe TopicsBulkAction do
 
     context "when the user can edit the topic" do
       it "changes the category and returns the topic_id" do
-        tba = TopicsBulkAction.new(topic.user, [topic.id], type: 'change_category', category_name: category.name)
+        tba = TopicsBulkAction.new(topic.user, [topic.id], type: 'change_category', category_id: category.id)
         topic_ids = tba.perform!
         topic_ids.should == [topic.id]
         topic.reload
@@ -29,7 +29,7 @@ describe TopicsBulkAction do
     context "when the user can't edit the topic" do
       it "doesn't change the category" do
         Guardian.any_instance.expects(:can_edit?).returns(false)
-        tba = TopicsBulkAction.new(topic.user, [topic.id], type: 'change_category', category_name: category.name)
+        tba = TopicsBulkAction.new(topic.user, [topic.id], type: 'change_category', category_id: category.id)
         topic_ids = tba.perform!
         topic_ids.should == []
         topic.reload
diff --git a/spec/controllers/topics_controller_spec.rb b/spec/controllers/topics_controller_spec.rb
index e69c6b516..897c008f3 100644
--- a/spec/controllers/topics_controller_spec.rb
+++ b/spec/controllers/topics_controller_spec.rb
@@ -719,8 +719,8 @@ describe TopicsController do
         end
 
         it 'triggers a change of category' do
-          Topic.any_instance.expects(:change_category).with('incredible').returns(true)
-          xhr :put, :update, topic_id: @topic.id, slug: @topic.title, category: 'incredible'
+          Topic.any_instance.expects(:change_category_to_id).with(123).returns(true)
+          xhr :put, :update, topic_id: @topic.id, slug: @topic.title, category_id: 123
         end
 
         it "returns errors with invalid titles" do
@@ -729,8 +729,8 @@ describe TopicsController do
         end
 
         it "returns errors with invalid categories" do
-          Topic.any_instance.expects(:change_category).returns(false)
-          xhr :put, :update, topic_id: @topic.id, slug: @topic.title, category: ''
+          Topic.any_instance.expects(:change_category_to_id).returns(false)
+          xhr :put, :update, topic_id: @topic.id, slug: @topic.title
           expect(response).not_to be_success
         end
 
@@ -740,8 +740,8 @@ describe TopicsController do
           end
 
           it "can add a category to an uncategorized topic" do
-            Topic.any_instance.expects(:change_category).with('incredible').returns(true)
-            xhr :put, :update, topic_id: @topic.id, slug: @topic.title, category: 'incredible'
+            Topic.any_instance.expects(:change_category_to_id).with(456).returns(true)
+            xhr :put, :update, topic_id: @topic.id, slug: @topic.title, category_id: 456
             response.should be_success
           end
         end
diff --git a/spec/models/category_spec.rb b/spec/models/category_spec.rb
index f29c38331..04f88ee1b 100644
--- a/spec/models/category_spec.rb
+++ b/spec/models/category_spec.rb
@@ -236,7 +236,7 @@ describe Category do
     describe "trying to change the category topic's category" do
       before do
         @new_cat = Fabricate(:category, name: '2nd Category', user: @category.user)
-        @topic.change_category(@new_cat.name)
+        @topic.change_category_to_id(@new_cat.id)
         @topic.reload
         @category.reload
       end
diff --git a/spec/models/topic_spec.rb b/spec/models/topic_spec.rb
index fb41d5693..ca1b5676d 100644
--- a/spec/models/topic_spec.rb
+++ b/spec/models/topic_spec.rb
@@ -802,7 +802,7 @@ describe Topic do
       let(:category) { Fabricate(:category) }
 
       before do
-        topic.change_category(category.name)
+        topic.change_category_to_id(category.id)
       end
 
       it "creates a new revision" do
@@ -811,7 +811,7 @@ describe Topic do
 
       context "removing a category" do
         before do
-          topic.change_category(nil)
+          topic.change_category_to_id(nil)
         end
 
         it "creates a new revision" do
@@ -850,12 +850,12 @@ describe Topic do
     describe 'without a previous category' do
 
       it 'should not change the topic_count when not changed' do
-       lambda { @topic.change_category(@topic.category.name); @category.reload }.should_not change(@category, :topic_count)
+       lambda { @topic.change_category_to_id(@topic.category.id); @category.reload }.should_not change(@category, :topic_count)
       end
 
       describe 'changed category' do
         before do
-          @topic.change_category(@category.name)
+          @topic.change_category_to_id(@category.id)
           @category.reload
         end
 
@@ -867,14 +867,14 @@ describe Topic do
       end
 
       it "doesn't change the category when it can't be found" do
-        @topic.change_category('made up')
+        @topic.change_category_to_id(12312312)
         @topic.category_id.should == SiteSetting.uncategorized_category_id
       end
     end
 
     describe 'with a previous category' do
       before do
-        @topic.change_category(@category.name)
+        @topic.change_category_to_id(@category.id)
         @topic.reload
         @category.reload
       end
@@ -884,18 +884,18 @@ describe Topic do
       end
 
       it "doesn't change the topic_count when the value doesn't change" do
-        lambda { @topic.change_category(@category.name); @category.reload }.should_not change(@category, :topic_count)
+        lambda { @topic.change_category_to_id(@category.id); @category.reload }.should_not change(@category, :topic_count)
       end
 
       it "doesn't reset the category when given a name that doesn't exist" do
-        @topic.change_category('made up')
+        @topic.change_category_to_id(55556)
         @topic.category_id.should be_present
       end
 
       describe 'to a different category' do
         before do
           @new_category = Fabricate(:category, user: @user, name: '2nd category')
-          @topic.change_category(@new_category.name)
+          @topic.change_category_to_id(@new_category.id)
           @topic.reload
           @new_category.reload
           @category.reload
@@ -918,13 +918,13 @@ describe Topic do
         let!(:topic) { Fabricate(:topic, category: Fabricate(:category)) }
 
         it 'returns false' do
-          topic.change_category('').should eq(false) # don't use "be_false" here because it would also match nil
+          topic.change_category_to_id(nil).should eq(false) # don't use "be_false" here because it would also match nil
         end
       end
 
       describe 'when the category exists' do
         before do
-          @topic.change_category(nil)
+          @topic.change_category_to_id(nil)
           @category.reload
         end