diff --git a/CHANGELOG b/CHANGELOG
index d00d3fab9a..43411be3bf 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -15,6 +15,7 @@ v 8.8.3
   - Fix incorrect links on pipeline page when merge request created from fork.  !4376
   - Use downcased path to container repository as this is expected path by Docker. !4420
   - Fix wiki project clone address error (chujinjin). !4429
+  - Fix serious performance bug with rendering Markdown with InlineDiffFilter.  !4392
   - In search results, only show notes on confidential issues that the user has access to
 
 v 8.8.2
diff --git a/lib/banzai/filter/inline_diff_filter.rb b/lib/banzai/filter/inline_diff_filter.rb
index 9e75edd4d4..beb21b19ab 100644
--- a/lib/banzai/filter/inline_diff_filter.rb
+++ b/lib/banzai/filter/inline_diff_filter.rb
@@ -8,15 +8,19 @@ module Banzai
           next if has_ancestor?(node, IGNORED_ANCESTOR_TAGS)
 
           content = node.to_html
-          content = content.gsub(/(?:\[\-(.*?)\-\]|\{\-(.*?)\-\})/, '<span class="idiff left right deletion">\1\2</span>')
-          content = content.gsub(/(?:\[\+(.*?)\+\]|\{\+(.*?)\+\})/, '<span class="idiff left right addition">\1\2</span>')
+          html_content = inline_diff_filter(content)
 
-          next if html == content
+          next if content == html_content
 
-          node.replace(content)
+          node.replace(html_content)
         end
         doc
       end
+
+      def inline_diff_filter(text)
+        html_content = text.gsub(/(?:\[\-(.*?)\-\]|\{\-(.*?)\-\})/, '<span class="idiff left right deletion">\1\2</span>')
+        html_content.gsub(/(?:\[\+(.*?)\+\]|\{\+(.*?)\+\})/, '<span class="idiff left right addition">\1\2</span>')
+      end
     end
   end
 end