diff --git a/Gemfile b/Gemfile
index 3dac0c0b..d61c57aa 100644
--- a/Gemfile
+++ b/Gemfile
@@ -15,6 +15,9 @@ gem 'irb', require: false
 group :test do
   gem 'eventmachine' unless RUBY_PLATFORM =~ /mswin|mingw/
   gem 'rspec', '~> 3.2'
+
+  # Downgrade psych because old RuboCop can't use new Psych
+  gem 'psych', '~> 3.3.2'
   # https://github.com/bbatsov/rubocop/pull/4789
   gem 'rubocop', '~> 0.50.0'
 end
diff --git a/spec/mysql2/client_spec.rb b/spec/mysql2/client_spec.rb
index 1519e0f5..41fb834b 100644
--- a/spec/mysql2/client_spec.rb
+++ b/spec/mysql2/client_spec.rb
@@ -604,7 +604,7 @@ def run_gc
       end
       expect do
         @client.query("SELECT SLEEP(1)")
-      end.to raise_error(Mysql2::Error, /Lost connection to MySQL server/)
+      end.to raise_error(Mysql2::Error, /Lost connection/)
 
       if RUBY_PLATFORM !~ /mingw|mswin/
         expect do