diff --git a/library/cgi/escapeHTML_spec.rb b/library/cgi/escapeHTML_spec.rb
index dcbfebe720..421aac5d4a 100644
--- a/library/cgi/escapeHTML_spec.rb
+++ b/library/cgi/escapeHTML_spec.rb
@@ -6,6 +6,10 @@
     CGI.escapeHTML(%[& < > " ']).should == '&amp; &lt; &gt; &quot; &#39;'
   end
 
+  it "escapes invalid encoding" do
+    CGI.escapeHTML(%[<\xA4??>]).should == "&lt;\xA4??&gt;"
+  end
+
   it "does not escape any other characters" do
     chars = " !\#$%()*+,-./0123456789:;=?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~"
     CGI.escapeHTML(chars).should == chars