diff --git a/activerecord/test/cases/migration/foreign_key_test.rb b/activerecord/test/cases/migration/foreign_key_test.rb
index ad35d690bd..f8b1bf8c9d 100644
--- a/activerecord/test/cases/migration/foreign_key_test.rb
+++ b/activerecord/test/cases/migration/foreign_key_test.rb
@@ -225,7 +225,7 @@ module ActiveRecord
 
       def silence_stream(stream)
         old_stream = stream.dup
-        stream.reopen(RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ? 'NUL:' : '/dev/null')
+        stream.reopen(IO::NULL)
         stream.sync = true
         yield
       ensure
diff --git a/activerecord/test/cases/migration_test.rb b/activerecord/test/cases/migration_test.rb
index 5829ef2100..7c2d3e81d6 100644
--- a/activerecord/test/cases/migration_test.rb
+++ b/activerecord/test/cases/migration_test.rb
@@ -939,7 +939,7 @@ class CopyMigrationsTest < ActiveRecord::TestCase
 
   def silence_stream(stream)
     old_stream = stream.dup
-    stream.reopen(RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ? 'NUL:' : '/dev/null')
+    stream.reopen(IO::NULL)
     stream.sync = true
     yield
   ensure
diff --git a/railties/test/generators/generators_test_helper.rb b/railties/test/generators/generators_test_helper.rb
index 94099fcd2e..7c5183e6c8 100644
--- a/railties/test/generators/generators_test_helper.rb
+++ b/railties/test/generators/generators_test_helper.rb
@@ -52,7 +52,7 @@ module GeneratorsTestHelper
 
   def silence_stream(stream)
     old_stream = stream.dup
-    stream.reopen(RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ? 'NUL:' : '/dev/null')
+    stream.reopen(IO::NULL)
     stream.sync = true
     yield
   ensure
diff --git a/railties/test/isolation/abstract_unit.rb b/railties/test/isolation/abstract_unit.rb
index 39e8a5f756..17c3f979c0 100644
--- a/railties/test/isolation/abstract_unit.rb
+++ b/railties/test/isolation/abstract_unit.rb
@@ -341,7 +341,7 @@ class ActiveSupport::TestCase
 
   def silence_stream(stream)
     old_stream = stream.dup
-    stream.reopen(RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ? 'NUL:' : '/dev/null')
+    stream.reopen(IO::NULL)
     stream.sync = true
     yield
   ensure