diff --git a/lib/file_store/s3_store.rb b/lib/file_store/s3_store.rb
index 076ea2171ab..b2f9c20988b 100644
--- a/lib/file_store/s3_store.rb
+++ b/lib/file_store/s3_store.rb
@@ -91,7 +91,7 @@ module FileStore
       return url if SiteSetting.Upload.s3_cdn_url.blank?
       schema = url[/^(https?:)?\/\//, 1]
       folder = @s3_helper.s3_bucket_folder_path.nil? ? "" : "#{@s3_helper.s3_bucket_folder_path}/"
-      url.sub("#{schema}#{absolute_base_url}/#{folder}", "#{SiteSetting.Upload.s3_cdn_url}/")
+      url.sub("#{schema}#{absolute_base_url}/#{folder}", "#{SiteSetting.Upload.s3_cdn_url}#{Discourse.base_uri}/")
     end
 
     def cache_avatar(avatar, user_id)
diff --git a/spec/components/file_store/s3_store_spec.rb b/spec/components/file_store/s3_store_spec.rb
index 06948702dd7..99e46fe4ccc 100644
--- a/spec/components/file_store/s3_store_spec.rb
+++ b/spec/components/file_store/s3_store_spec.rb
@@ -282,4 +282,21 @@ describe FileStore::S3Store do
       assert_path("https://hello", nil)
     end
   end
+
+  describe '.cdn_url' do
+
+    it 'uses the correct path' do
+      url = "//s3-upload-bucket.s3-us-west-2.amazonaws.com/livechat/original/1X/2252ae522257fc537351e47bbdd34698936b6c38.jpeg"
+      expect(store.cdn_url(url)).to end_with('/livechat/original/1X/2252ae522257fc537351e47bbdd34698936b6c38.jpeg')
+    end
+
+    it 'supports subfolder' do
+      SiteSetting.s3_upload_bucket = 's3-upload-bucket/livechat/community'
+      GlobalSetting.stubs(:relative_url_root).returns('/community')
+      Discourse.stubs(:base_uri).returns("/community")
+      url = "//s3-upload-bucket.s3-us-west-2.amazonaws.com/livechat/community/original/1X/2252ae522257fc537351e47bbdd34698936b6c38.jpeg"
+      expect(store.cdn_url(url)).to end_with('/livechat/community/original/1X/2252ae522257fc537351e47bbdd34698936b6c38.jpeg')
+    end
+  end
+
 end