diff --git a/app/assets/javascripts/discourse/routes/build-category-route.js.es6 b/app/assets/javascripts/discourse/routes/build-category-route.js.es6
index f9792401565..14bc77f8a5f 100644
--- a/app/assets/javascripts/discourse/routes/build-category-route.js.es6
+++ b/app/assets/javascripts/discourse/routes/build-category-route.js.es6
@@ -67,9 +67,6 @@ export default (filter, params) => {
       return findTopicList(this.store, this.topicTrackingState, listFilter, findOpts, extras).then(list => {
         TopicList.hideUniformCategory(list, category);
         this.set('topics', list);
-        if (list.topic_list.tags) {
-          Discourse.Site.currentProp('top_tags', list.topic_list.tags);
-        }
         return list;
       });
     },
diff --git a/app/assets/javascripts/discourse/routes/build-topic-route.js.es6 b/app/assets/javascripts/discourse/routes/build-topic-route.js.es6
index 43c920535ee..d7a2116bee6 100644
--- a/app/assets/javascripts/discourse/routes/build-topic-route.js.es6
+++ b/app/assets/javascripts/discourse/routes/build-topic-route.js.es6
@@ -54,6 +54,9 @@ function findTopicList(store, tracking, filter, filterParams, extras) {
       tracking.trackIncoming(list.filter);
     }
     Discourse.Session.currentProp('topicList', list);
+    if (list.topic_list && list.topic_list.tags) {
+      Discourse.Site.currentProp('top_tags', list.topic_list.tags);
+    }
     return list;
   });
 }
diff --git a/app/assets/javascripts/discourse/routes/tags-show.js.es6 b/app/assets/javascripts/discourse/routes/tags-show.js.es6
index bed2d5b36c9..c82acb9eabb 100644
--- a/app/assets/javascripts/discourse/routes/tags-show.js.es6
+++ b/app/assets/javascripts/discourse/routes/tags-show.js.es6
@@ -75,9 +75,6 @@ export default Discourse.Route.extend({
     return findTopicList(this.store, this.topicTrackingState, params.filter, params, {}).then(function(list) {
       controller.set('list', list);
       controller.set('canCreateTopic', list.get('can_create_topic'));
-      if (list.topic_list.tags) {
-        Discourse.Site.currentProp('top_tags', list.topic_list.tags);
-      }
       controller.set('loading', false);
     });
   },
diff --git a/app/models/tag.rb b/app/models/tag.rb
index 78652a1871a..f6d4661b2fe 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -23,10 +23,19 @@ class Tag < ActiveRecord::Base
                              .where("topics.category_id = ?", category.id)
   end
 
-  def self.top_tags(limit_arg: nil, category: nil)
+  def self.top_tags(limit_arg: nil, category: nil, guardian: nil)
     limit = limit_arg || SiteSetting.max_tags_in_filter_list
+    scope_category_ids = (guardian||Guardian.new).allowed_category_ids
 
-    tags = DiscourseTagging.filter_allowed_tags(tags_by_count_query(limit: limit), nil, category: category)
+    if category
+      scope_category_ids &= ([category.id] + category.subcategories.pluck(:id))
+    end
+
+    tags = DiscourseTagging.filter_allowed_tags(
+      tags_by_count_query(limit: limit).where("topics.category_id in (?)", scope_category_ids),
+      nil, # Don't pass guardian. You might not be able to use some tags, but should still be able to see where they've been used.
+      category: category
+    )
 
     tags.count.map {|name, _| name}
   end
diff --git a/app/models/topic_list.rb b/app/models/topic_list.rb
index 8fda6ede868..e0b3fd8353b 100644
--- a/app/models/topic_list.rb
+++ b/app/models/topic_list.rb
@@ -31,6 +31,7 @@ class TopicList
 
   def tags
     opts = @category ? { category: @category } : {}
+    opts[:guardian] = Guardian.new(@current_user)
     Tag.top_tags(opts)
   end
 
diff --git a/app/serializers/site_serializer.rb b/app/serializers/site_serializer.rb
index c9e3b87cee1..217f7885438 100644
--- a/app/serializers/site_serializer.rb
+++ b/app/serializers/site_serializer.rb
@@ -111,7 +111,7 @@ class SiteSerializer < ApplicationSerializer
   end
 
   def top_tags
-    Tag.top_tags
+    Tag.top_tags(guardian: scope)
   end
 
   def wizard_required
diff --git a/spec/models/tag_spec.rb b/spec/models/tag_spec.rb
index 1a42a27cea0..d09cd732448 100644
--- a/spec/models/tag_spec.rb
+++ b/spec/models/tag_spec.rb
@@ -54,6 +54,43 @@ describe Tag do
       expect(described_class.top_tags.sort).to eq(@tags.map(&:name).sort)
     end
 
+    context "with categories" do
+      before do
+        make_some_tags(count: 4) # one tag that isn't used
+        @category1 = Fabricate(:category)
+        @private_category = Fabricate(:category)
+        @private_category.set_permissions(:admins => :full)
+        @private_category.save!
+        @topics = []
+        @topics << Fabricate(:topic, category: @category1, tags: [@tags[0]])
+        @topics << Fabricate(:topic, tags: [@tags[1]])
+        @topics << Fabricate(:topic, category: @private_category, tags: [@tags[2]])
+      end
+
+      it "doesn't return tags that have only been used in private category to anon" do
+        expect(described_class.top_tags.sort).to eq([@tags[0].name, @tags[1].name].sort)
+      end
+
+      it "returns tags used in private category to those who can see that category" do
+        expect(described_class.top_tags(guardian: Guardian.new(Fabricate(:admin))).sort).to eq([@tags[0].name, @tags[1].name, @tags[2].name].sort)
+      end
+
+      it "returns tags scoped to a given category" do
+        expect(described_class.top_tags(category: @category1).sort).to eq([@tags[0].name].sort)
+        expect(described_class.top_tags(category: @private_category, guardian: Guardian.new(Fabricate(:admin))).sort).to eq([@tags[2].name].sort)
+      end
+
+      it "returns tags from sub-categories too" do
+        sub_category = Fabricate(:category, parent_category_id: @category1.id)
+        Fabricate(:topic, category: sub_category, tags: [@tags[1]])
+        expect(described_class.top_tags(category: @category1).sort).to eq([@tags[0].name, @tags[1].name].sort)
+      end
+
+      it "returns nothing if category arg is private to you" do
+        expect(described_class.top_tags(category: @private_category)).to be_empty
+      end
+    end
+
     context "with category-specific tags" do
       before do
         make_some_tags(count: 3)
diff --git a/spec/models/topic_list_spec.rb b/spec/models/topic_list_spec.rb
index 38a13515d97..f8fbe55c56a 100644
--- a/spec/models/topic_list_spec.rb
+++ b/spec/models/topic_list_spec.rb
@@ -61,11 +61,11 @@ describe TopicList do
         expect(TopicList.new('latest', other_topic.user, [other_topic]).tags.sort).to eq([tag.name, other_tag.name].sort)
       end
 
-      it "with another category with no tags, should return exclude tags restricted to other categories" do
+      it "with another category with no tags, should return no tags" do
         other_category = Fabricate(:category)
         topic3 = Fabricate(:topic, category: other_category)
         list = TopicList.new('latest', topic3.user, [topic3], { category: other_category.id, category_id: other_category.id })
-        expect(list.tags).to eq([other_tag.name])
+        expect(list.tags).to be_empty
       end
     end
   end