diff --git a/bootstraptest/test_knownbug.rb b/bootstraptest/test_knownbug.rb
index 917091df0c..9949ac5f29 100644
--- a/bootstraptest/test_knownbug.rb
+++ b/bootstraptest/test_knownbug.rb
@@ -53,3 +53,6 @@ assert_normal_exit %q{
 assert_normal_exit %q{
   "abc".gsub(/./, "a" => "z")
 }
+assert_normal_exit %q{
+  Encoding.compatible?("",0)
+}