diff --git a/prelude.rb b/prelude.rb
index f9bb7451f813e7..740aba5b793d0b 100644
--- a/prelude.rb
+++ b/prelude.rb
@@ -99,7 +99,7 @@ def read_nonblock(len, buf = nil, exception: true)
   #
   #   # write_nonblock writes only 65536 bytes and return 65536.
   #   # (The pipe size is 65536 bytes on this environment.)
-  #   s = "a"  #100000
+  #   s = "a" * 100000
   #   p w.write_nonblock(s)     #=> 65536
   #
   #   # write_nonblock cannot write a byte and raise EWOULDBLOCK (EAGAIN).