Issue #21199 has been updated by mame (Yusuke Endoh). Status changed from Open to Feedback Note that `date` and `date2` are equal in your reproduction code. ```ruby require 'date' require 'psych' date = Date.new(1582, 10, 4) p "date=#{date.inspect}" str = Psych.dump(date, permitted_classes: [Date]) p "str=#{str}" date2 = Psych.load(str, permitted_classes: [Date]) p "date2=#{date2.inspect}" p date == date2 #=> true ``` The issue is that YAML cannot retain calendar information. When Psych serializes a `Date` object, it converts it to `Date::GREGORIAN` (the proleptic Gregorian calendar). As a result, the serialized YAML contains `--- 1582-10-14`, which is intentional. When deserializing a `Date` from YAML, a `Date::GREGORIAN` Date object is generated. I believe it would be possible to convert it to an `Date::ITALY` Date object by default. However, consider a case where a user manually writes `--- 1582-10-14` in YAML and loads it with Psych. They would then get `Date.new(1582, 10, 4)`, which could be an unexpected result. For this reason, I thinkg the current behavior is unavoidable. If you have a specific proposal on how to fix it, please write it. ---------------------------------------- Bug #21199: Psych.dump and load on Date before 1582-10-15 https://bugs.ruby-lang.org/issues/21199#change-112448 * Author: fitmap (Justin Peal) * Status: Feedback * ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x64-mingw-ucrt] * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- The code is: require 'date' require 'psych' date = Date.new(1582, 10, 4) p "date=#{date.inspect}" str = Psych.dump(date, permitted_classes: [Date]) p "str=#{str}" date2 = Psych.load(str, permitted_classes: [Date]) p "date2=#{date2.inspect}" The output is: "date=#<Date: 1582-10-04 ((2299160j,0s,0n),+0s,2299161j)>" "str=--- 1582-10-14\n" "date2=#<Date: 1582-10-14 ((2299160j,0s,0n),+0s,-Infj)>" -- https://bugs.ruby-lang.org/