diff --git a/lib/discourse_chat/provider/slack/slack_provider.rb b/lib/discourse_chat/provider/slack/slack_provider.rb
index d351354..355c3a9 100644
--- a/lib/discourse_chat/provider/slack/slack_provider.rb
+++ b/lib/discourse_chat/provider/slack/slack_provider.rb
@@ -23,7 +23,7 @@ module DiscourseChat::Provider::SlackProvider
   end
 
   def self.excerpt(post, max_length = SiteSetting.chat_integration_slack_excerpt_length)
-    doc = Nokogiri::HTML.fragment(post.excerpt(max_length,
+    doc = Nokogiri::HTML5.fragment(post.excerpt(max_length,
       remap_emoji: true,
       keep_onebox_source: true
     ))