diff --git a/lib/rubocop/isucon/memorize_methods.rb b/lib/rubocop/isucon/memorize_methods.rb
index 981b48e0..17597207 100644
--- a/lib/rubocop/isucon/memorize_methods.rb
+++ b/lib/rubocop/isucon/memorize_methods.rb
@@ -30,7 +30,7 @@ def #{method_name}_with_cache
           end
         RUBY
 
-        alias_method "#{method_name}_without_cache", method_name
+        alias_method :"#{method_name}_without_cache", method_name
         alias_method method_name, "#{method_name}_with_cache"
       end
     end
diff --git a/rubocop-isucon.gemspec b/rubocop-isucon.gemspec
index 14603c70..4262af90 100644
--- a/rubocop-isucon.gemspec
+++ b/rubocop-isucon.gemspec
@@ -38,7 +38,7 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency "activerecord", ">= 6.1.0"
   spec.add_runtime_dependency "gda", "!= 1.1.2"
   spec.add_runtime_dependency "rubocop", ">= 1.49.0"
-  spec.add_runtime_dependency "rubocop-performance"
+  spec.add_runtime_dependency "rubocop-performance", ">= 1.20.0"
 
   spec.add_development_dependency "benchmark-ips"
   spec.add_development_dependency "pry-byebug"