Issue #9537 has been reported by Masahiro Nakagawa.

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Backport #9537: backport r45047
https://bugs.ruby-lang.org/issues/9537

* Author: Masahiro Nakagawa
* Status: Open
* Priority: Normal
* Assignee: 
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Related issue: https://bugs.ruby-lang.org/issues/9525

This problem is a big issue for Fluentd. 
Please backport this commit to Ruby 2.0.



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