diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index e395d75e6d..13261eacdd 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -3369,7 +3369,7 @@ CODE
     assert_same(str, -str)
 
     bar = -%w(b a r).join('')
-    assert_same(str, bar, "uminus deduplicates [Feature #13077] #{ObjectSpace.dump(bar)}")
+    assert_same(str, bar, "uminus deduplicates [Feature #13077] str: #{ObjectSpace.dump(str)} bar: #{ObjectSpace.dump(bar)}")
   end
 
   def test_uminus_frozen