diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 9e87344d..5b05c69d 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: [ '3.0', 2.7, 2.6, 2.5, 2.4, head, jruby-9.2.17.0, jruby-head ]
+        ruby: [ '3.0', 2.7, 2.6, 2.5, head, jruby-9.2.17.0, jruby-head ]
     steps:
     - uses: actions/checkout@v2
     - name: Set up Ruby
diff --git a/lib/racc/statetransitiontable.rb b/lib/racc/statetransitiontable.rb
index 4252ba01..4d542872 100644
--- a/lib/racc/statetransitiontable.rb
+++ b/lib/racc/statetransitiontable.rb
@@ -12,12 +12,6 @@
 
 require 'racc/parser'
 
-unless Object.method_defined?(:funcall)
-  class Object
-    alias funcall __send__
-  end
-end
-
 module Racc
 
   StateTransitionTable = Struct.new(:action_table,
@@ -300,9 +294,9 @@ def define_actions(c)
       c.module_eval "def _reduce_none(vals, vstack) vals[0] end"
       @grammar.each do |rule|
         if rule.action.empty?
-          c.funcall(:alias_method, "_reduce_#{rule.ident}", :_reduce_none)
+          c.alias_method("_reduce_#{rule.ident}", :_reduce_none)
         else
-          c.funcall(:define_method, "_racc_action_#{rule.ident}", &rule.action.proc)
+          c.define_method("_racc_action_#{rule.ident}", &rule.action.proc)
           c.module_eval(<<-End, __FILE__, __LINE__ + 1)
             def _reduce_#{rule.ident}(vals, vstack)
               _racc_action_#{rule.ident}(*vals)
diff --git a/racc.gemspec b/racc.gemspec
index 1157a8f6..cf98f93b 100644
--- a/racc.gemspec
+++ b/racc.gemspec
@@ -89,7 +89,7 @@ DESC
     "doc/en/Overview-of-racc.md"
   ]
   s.require_paths = ["lib"]
-  s.required_rubygems_version = Gem::Requirement.new(">= 0") if s.respond_to? :required_rubygems_version=
+  s.required_ruby_version = ">= 2.5"
   s.rdoc_options = ["--main", "README.rdoc"]
   s.extra_rdoc_files = [
     "README.ja.rdoc", "README.rdoc",