diff --git a/activesupport/test/clean_logger_test.rb b/activesupport/test/clean_logger_test.rb
index 4e3e69b74e..afcd8c1268 100644
--- a/activesupport/test/clean_logger_test.rb
+++ b/activesupport/test/clean_logger_test.rb
@@ -20,7 +20,7 @@ def test_datetime_format
     @logger.formatter.datetime_format = "%Y-%m-%d"
     @logger.debug "debug"
     assert_equal "%Y-%m-%d", @logger.formatter.datetime_format
-    assert_match(/D, \[\d\d\d\d-\d\d-\d\d#\d+\] DEBUG -- : debug/, @out.string)
+    assert_match(/D, \[\d\d\d\d-\d\d-\d\d[ ]?#\d+\] DEBUG -- : debug/, @out.string)
   end
 
   def test_nonstring_formatting