diff --git a/test/-ext-/symbol/test_inadvertent_creation.rb b/test/-ext-/symbol/test_inadvertent_creation.rb
index b1be3f6744..7c0aaa89f0 100644
--- a/test/-ext-/symbol/test_inadvertent_creation.rb
+++ b/test/-ext-/symbol/test_inadvertent_creation.rb
@@ -4,7 +4,7 @@ require "-test-/symbol/symbol"
 module Test_Symbol
   class TestInadvertent < Test::Unit::TestCase
     def noninterned_name(prefix = "")
-      prefix += "_#{Thread.current.object_id.to_s(36)}"
+      prefix += "_#{Thread.current.object_id.to_s(36).tr('-', '_')}"
       begin
         name = "#{prefix}_#{rand(0x1000).to_s(16)}_#{Time.now.usec}"
       end while Bug::Symbol.interned?(name)