diff --git a/Gemfile b/Gemfile
index 03f82f81..860a1c47 100644
--- a/Gemfile
+++ b/Gemfile
@@ -4,3 +4,11 @@ source "https://rubygems.org"
 gemspec
 
 gem "rake", ">= 12.3.3"
+
+# i18n 1.15.0 started using Fiber storage (`Fiber.[]`), which only exists on
+# Ruby 3.2+, so on older Rubies ActiveSupport blew up loading it with
+# `NoMethodError: undefined method '[]' for Fiber:Class` (fixed upstream in
+# 1.15.2). Gemfile.lock is gitignored, so CI resolves i18n fresh each run and is
+# at the mercy of such transient bad releases on the pre-3.2 matrix. Keep those
+# (EOL-track) Rubies pinned to the stable 1.14 line for a deterministic build.
+gem "i18n", "< 1.15" if RUBY_VERSION < "3.2"