[ruby-core:127157] [Ruby Bug#22452] `rb_equal` returns true for `NaN == NaN`

17 Oct 2026

      Issue #22452 has been reported by byroot (Jean Boussier).

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Bug #22452: `rb_equal` returns true for `NaN == NaN`
https://bugs.ruby-lang.org/issues/22452

* Author: byroot (Jean Boussier)
* Status: Open
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
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I noticed this while trying to cleanup and simplify `rb_equal`.

```ruby
...
...
Float::NAN == Float::NAN
=> false
[Float::NAN].index(Float::NAN)
=> 0

I would expect it to return `nil`.

This bug is present on all Ruby versions, except for 2.1 to 2.4. JRuby seem to have the same behavior, but TruffleRuby correctly returns`nil`

The bug seem to have been re-introduced by 6e0e067de31511cebec01d176f628442371db879

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