diff --git a/app/models/dmail.rb b/app/models/dmail.rb
index 688e50c69..06e84ae3f 100644
--- a/app/models/dmail.rb
+++ b/app/models/dmail.rb
@@ -104,7 +104,7 @@ class Dmail < ActiveRecord::Base
 
     def title_matches(query)
       query = "*#{query}*" unless query =~ /\*/
-      where("lower(dmails.title) LIKE ?", query.to_escaped_for_sql_like)
+      where("lower(dmails.title) LIKE ?", query.mb_chars.downcase.to_escaped_for_sql_like)
     end
 
     def search_message(query)
diff --git a/test/unit/dmail_test.rb b/test/unit/dmail_test.rb
index ec89c655c..b97b4aacf 100644
--- a/test/unit/dmail_test.rb
+++ b/test/unit/dmail_test.rb
@@ -78,6 +78,9 @@ class DmailTest < ActiveSupport::TestCase
         matches = Dmail.search(title_matches: "x")
         assert_equal([dmail.id], matches.map(&:id))
 
+        matches = Dmail.search(title_matches: "X")
+        assert_equal([dmail.id], matches.map(&:id))
+
         matches = Dmail.search(message_matches: "xxx")
         assert_equal([dmail.id], matches.map(&:id))