diff --git a/test/irb/test_history.rb b/test/irb/test_history.rb
index 84f043892..7a17491d8 100644
--- a/test/irb/test_history.rb
+++ b/test/irb/test_history.rb
@@ -149,7 +149,7 @@ def test_history_concurrent_use_not_present
     def test_history_different_encodings
       IRB.conf[:SAVE_HISTORY] = 2
       Encoding.default_external = Encoding::US_ASCII
-      locale = IRB::Locale.new("C")
+      locale = IRB::Locale.new("en_US.ASCII")
       assert_history(<<~EXPECTED_HISTORY.encode(Encoding::US_ASCII), <<~INITIAL_HISTORY.encode(Encoding::UTF_8), <<~INPUT, locale: locale)
         ????
         exit