diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index f16573682b..b5d69d9ba4 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -2446,6 +2446,7 @@ End
   end
 
   def test_puts_parallel
+    skip "not portable"
     pipe(proc do |w|
       threads = []
       100.times do