diff --git a/lib/gitlab/markdown.rb b/lib/gitlab/markdown.rb
index f9125e0390a..4fc0c392cac 100644
--- a/lib/gitlab/markdown.rb
+++ b/lib/gitlab/markdown.rb
@@ -48,6 +48,9 @@ module Gitlab
     def gfm(text, html_options = {})
       return text if text.nil?
 
+      # prevents the string supplied through the _text_ argument to be altered
+      text = text.dup
+
       @html_options = html_options
 
       # Extract pre blocks so they are not altered