diff --git a/activesupport/test/core_ext/string_ext_test.rb b/activesupport/test/core_ext/string_ext_test.rb
index bb865cae91..38b344b885 100644
--- a/activesupport/test/core_ext/string_ext_test.rb
+++ b/activesupport/test/core_ext/string_ext_test.rb
@@ -381,6 +381,18 @@ class OutputSafetyTest < ActiveSupport::TestCase
     assert !@other_combination.html_safe?
   end
 
+  test "Escapes special HTML/XML characters" do
+    @other_string = "other".html_safe
+    @combination = @other_string + "<foo>&\"'"
+    @other_combination = @string + "<foo>&\"'"
+
+    assert_equal "other&lt;foo&gt;&amp;&quot;&apos;", @combination
+    assert_equal "hello<foo>&\"'", @other_combination
+
+    assert @combination.html_safe?
+    assert !@other_combination.html_safe?
+  end
+
   test "Concatting safe onto unsafe yields unsafe" do
     @other_string = "other"