diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index bb878ea148..ad9e4fa08f 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -3081,7 +3081,7 @@ End
 
       # try to raise RLIM_NOFILE to >FD_SETSIZE
       begin
-        Process.setrlimit(Process::RLIMIT_NOFILE, fd_setsize+10)
+        Process.setrlimit(Process::RLIMIT_NOFILE, fd_setsize+20)
       rescue Errno::EPERM
         exit 0
       end