diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index 13261eacdd..ebe85dac82 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -3358,7 +3358,7 @@ CODE
 
     require 'objspace'
 
-    str = "bar".freeze
+    str = "test_uplus_minus_str".freeze
     assert_includes ObjectSpace.dump(str), '"fstring":true'
 
     assert_predicate(str, :frozen?)
@@ -3368,7 +3368,7 @@ CODE
     assert_not_same(str, +str)
     assert_same(str, -str)
 
-    bar = -%w(b a r).join('')
+    bar = -%w(test uplus minus str).join('_')
     assert_same(str, bar, "uminus deduplicates [Feature #13077] str: #{ObjectSpace.dump(str)} bar: #{ObjectSpace.dump(bar)}")
   end