diff --git a/Gemfile b/Gemfile
index 78b50ff..aa38f67 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,4 +5,5 @@ gemspec
 gem "rake"
 gem "test-unit"
 gem "test-unit-ruby-core"
+gem "power_assert", "~> 2.0" if RUBY_VERSION < '3.1' # https://github.com/ruby/power_assert/pull/61
 gem "webrick"