diff --git a/app/assets/javascripts/discourse/components/d-editor.js.es6 b/app/assets/javascripts/discourse/components/d-editor.js.es6
index 631429f37e7..6cf61237010 100644
--- a/app/assets/javascripts/discourse/components/d-editor.js.es6
+++ b/app/assets/javascripts/discourse/components/d-editor.js.es6
@@ -255,7 +255,7 @@ export default Ember.Component.extend({
       template: template,
       key: '#',
       transformComplete(category) {
-        return category.get('slug');
+        return Category.slugFor(category, ":");
       },
       dataSource(term) {
         return Category.search(term);
diff --git a/app/assets/javascripts/discourse/dialects/category_hashtag_dialect.js b/app/assets/javascripts/discourse/dialects/category_hashtag_dialect.js
index 4beb7ab537e..3242e9667df 100644
--- a/app/assets/javascripts/discourse/dialects/category_hashtag_dialect.js
+++ b/app/assets/javascripts/discourse/dialects/category_hashtag_dialect.js
@@ -4,7 +4,7 @@
 **/
 Discourse.Dialect.inlineRegexp({
   start: '#',
-  matcher: /^#([\w-]{1,50})/i,
+  matcher: /^#([\w-:]{1,50})/i,
   spaceOrTagBoundary: true,
 
   emitter: function(matches) {
diff --git a/app/assets/javascripts/discourse/models/category.js.es6 b/app/assets/javascripts/discourse/models/category.js.es6
index e507419c0ef..91d5c60dfec 100644
--- a/app/assets/javascripts/discourse/models/category.js.es6
+++ b/app/assets/javascripts/discourse/models/category.js.es6
@@ -205,14 +205,14 @@ Category.reopenClass({
     return _uncategorized;
   },
 
-  slugFor(category) {
+  slugFor(category, separator = "/") {
     if (!category) return "";
 
     const parentCategory = Em.get(category, 'parentCategory');
     let result = "";
 
     if (parentCategory) {
-      result = Category.slugFor(parentCategory) + "/";
+      result = Category.slugFor(parentCategory) + separator;
     }
 
     const id = Em.get(category, 'id'),
diff --git a/app/controllers/category_hashtags_controller.rb b/app/controllers/category_hashtags_controller.rb
index 6e78a92ec73..ca4a1f70062 100644
--- a/app/controllers/category_hashtags_controller.rb
+++ b/app/controllers/category_hashtags_controller.rb
@@ -5,8 +5,10 @@ class CategoryHashtagsController < ApplicationController
     category_slugs = params[:category_slugs]
     category_slugs.each(&:downcase!)
 
-    valid_categories = Category.secured(guardian).where(slug: category_slugs).map do |category|
-      { slug: category.slug, url: category.url_with_id }
+    ids = category_slugs.map { |category_slug| Category.query_from_hashtag_slug(category_slug).try(:id) }
+
+    valid_categories = Category.secured(guardian).where(id: ids).map do |category|
+      { slug: category.hashtag_slug, url: category.url_with_id }
     end.compact
 
     render json: { valid: valid_categories }
diff --git a/app/models/category.rb b/app/models/category.rb
index 7ada616b828..96127678008 100644
--- a/app/models/category.rb
+++ b/app/models/category.rb
@@ -5,6 +5,7 @@ class Category < ActiveRecord::Base
 
   include Positionable
   include HasCustomFields
+  include CategoryHashtag
 
   belongs_to :topic, dependent: :destroy
   belongs_to :topic_only_relative_url,
@@ -398,8 +399,8 @@ SQL
     @@url_cache.clear
   end
 
-  def full_slug
-    url[3..-1].gsub("/", "-")
+  def full_slug(separator = "-")
+    url[3..-1].gsub("/", separator)
   end
 
   def url
diff --git a/app/models/concerns/category_hashtag.rb b/app/models/concerns/category_hashtag.rb
new file mode 100644
index 00000000000..fe97b02525f
--- /dev/null
+++ b/app/models/concerns/category_hashtag.rb
@@ -0,0 +1,23 @@
+module CategoryHashtag
+  extend ActiveSupport::Concern
+
+  SEPARATOR = ":".freeze
+
+  class_methods do
+    def query_from_hashtag_slug(category_slug)
+      parent_slug, child_slug = category_slug.split(":", 2)
+
+      category = Category.where(slug: parent_slug, parent_category_id: nil)
+
+      if child_slug
+        Category.where(slug: child_slug, parent_category_id: category.pluck(:id).first).first
+      else
+        category.first
+      end
+    end
+  end
+
+  def hashtag_slug
+    full_slug(SEPARATOR)
+  end
+end
diff --git a/lib/pretty_text.rb b/lib/pretty_text.rb
index 126f3358c2e..927f8ecd70d 100644
--- a/lib/pretty_text.rb
+++ b/lib/pretty_text.rb
@@ -49,9 +49,8 @@ module PrettyText
     end
 
     def category_hashtag_lookup(category_slug)
-      if category_slug
-        category = Category.find_by_slug(category_slug)
-        return ['category', category.url_with_id] if category
+      if category = Category.query_from_hashtag_slug(category_slug)
+        ['category', category.url_with_id]
       else
         nil
       end
diff --git a/spec/components/concern/category_hashtag_spec.rb b/spec/components/concern/category_hashtag_spec.rb
new file mode 100644
index 00000000000..3fe10ba84cb
--- /dev/null
+++ b/spec/components/concern/category_hashtag_spec.rb
@@ -0,0 +1,26 @@
+require 'rails_helper'
+
+describe CategoryHashtag do
+  describe '#query_from_hashtag_slug' do
+    let(:parent_category) { Fabricate(:category) }
+    let(:child_category) { Fabricate(:category, parent_category: parent_category) }
+
+    it "should return the right result for a parent category slug" do
+      expect(Category.query_from_hashtag_slug(parent_category.slug))
+        .to eq(parent_category)
+    end
+
+    it "should return the right result for a parent and child category slug" do
+      expect(Category.query_from_hashtag_slug("#{parent_category.slug}:#{child_category.slug}"))
+        .to eq(child_category)
+    end
+
+    it "should return nil for incorrect parent category slug" do
+      expect(Category.query_from_hashtag_slug("random-slug")).to eq(nil)
+    end
+
+    it "should return nil for incorrect parent and child category slug" do
+      expect(Category.query_from_hashtag_slug("random-slug:random-slug")).to eq(nil)
+    end
+  end
+end
diff --git a/spec/components/pretty_text_spec.rb b/spec/components/pretty_text_spec.rb
index f9cd29081c3..dabe28405fc 100644
--- a/spec/components/pretty_text_spec.rb
+++ b/spec/components/pretty_text_spec.rb
@@ -390,7 +390,7 @@ HTML
     end
 
     it "doesn't replace unicode emoji if emoji is disabled" do
-      SiteSetting.enable_emoji = false 
+      SiteSetting.enable_emoji = false
       expect(PrettyText.cook("💣")).not_to match(/\:bomb\:/)
     end
   end
diff --git a/spec/controllers/category_hashtags_controller_spec.rb b/spec/controllers/category_hashtags_controller_spec.rb
index 01d5eeb74f1..e5f1515614c 100644
--- a/spec/controllers/category_hashtags_controller_spec.rb
+++ b/spec/controllers/category_hashtags_controller_spec.rb
@@ -12,7 +12,7 @@ describe CategoryHashtagsController do
         xhr :get, :check, category_slugs: [category.slug, 'none']
 
         expect(JSON.parse(response.body)).to eq(
-          { "valid" => [{ "slug" => category.slug, "url" => category.url_with_id }] }
+          { "valid" => [{ "slug" => category.hashtag_slug, "url" => category.url_with_id }] }
         )
       end
 
@@ -32,7 +32,7 @@ describe CategoryHashtagsController do
         xhr :get, :check, category_slugs: [private_category.slug]
 
         expect(JSON.parse(response.body)).to eq(
-          { "valid" => [{ "slug" => private_category.slug, "url" => private_category.url_with_id }] }
+          { "valid" => [{ "slug" => private_category.hashtag_slug, "url" => private_category.url_with_id }] }
         )
       end
     end