diff --git a/lib/redmine/wiki_formatting/common_mark/external_links_filter.rb b/lib/redmine/wiki_formatting/common_mark/external_links_filter.rb
index d2ea3fafa..4c25a7b13 100644
--- a/lib/redmine/wiki_formatting/common_mark/external_links_filter.rb
+++ b/lib/redmine/wiki_formatting/common_mark/external_links_filter.rb
@@ -31,7 +31,7 @@ module Redmine
             next unless url
             next if url.starts_with?("/") || url.starts_with?("#") || !url.include?(':')
 
-            scheme = URI.parse(url).scheme
+            scheme = URI.parse(url).scheme rescue nil
             next if scheme.blank?
 
             klass = node["class"].presence