diff --git a/.github/workflows/actions.yml b/.github/workflows/actions.yml
index 4728c2a..a699e0b 100644
--- a/.github/workflows/actions.yml
+++ b/.github/workflows/actions.yml
@@ -12,10 +12,10 @@ jobs:
         image: mysql
     strategy:
       matrix:
-        ruby: [ '2.5', '2.6', '2.7', '3.0', '3.1', '3.2' ]
+        ruby: [ '2.7', '3.0', '3.1', '3.2' ]
         task: [ 'spec' ]
         include:
-        - ruby: 2.5 # keep in sync with lowest version
+        - ruby: 2.7 # keep in sync with lowest version
           task: rubocop
     name: ${{ matrix.ruby }} rake ${{ matrix.task }}
     steps:
diff --git a/.rubocop.yml b/.rubocop.yml
index 9fa1d8c..c7762da 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -4,17 +4,11 @@ require:
 
 AllCops:
   NewCops: enable
-  TargetRubyVersion: 2.5
+  TargetRubyVersion: 2.7
 
 Style/StringLiterals:
   Enabled: false
 
-Style/StringLiteralsInInterpolation:
-  Enabled: false
-
-Lint/AmbiguousRegexpLiteral:
-  Enabled: false
-
 Bundler/OrderedGems:
   Enabled: false
 
@@ -65,9 +59,6 @@ Style/SymbolArray:
 Style/GuardClause:
   Enabled: false
 
-Lint/AssignmentInCondition:
-  Enabled: false
-
 Style/EmptyElse:
   Enabled: false
 
diff --git a/Gemfile.lock b/Gemfile.lock
index 1b5404d..faf2145 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -23,14 +23,20 @@ GEM
     diff-lcs (1.5.0)
     i18n (1.10.0)
       concurrent-ruby (~> 1.0)
+    json (2.7.1)
+    json (2.7.1-java)
+    language_server-protocol (3.17.0.3)
     minitest (5.15.0)
-    mysql2 (0.5.3)
-    parser (3.1.1.0)
+    mysql2 (0.5.6)
+    parser (3.3.0.5)
       ast (~> 2.4.1)
+      racc
+    racc (1.7.3)
+    racc (1.7.3-java)
     rainbow (3.1.1)
     rake (13.0.6)
-    regexp_parser (2.2.1)
-    rexml (3.2.5)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
     rspec (3.11.0)
       rspec-core (~> 3.11.0)
       rspec-expectations (~> 3.11.0)
@@ -48,26 +54,28 @@ GEM
     rspec-rerun (1.1.0)
       rspec (~> 3.0)
     rspec-support (3.11.0)
-    rubocop (1.26.0)
+    rubocop (1.62.1)
+      json (~> 2.3)
+      language_server-protocol (>= 3.17.0)
       parallel (~> 1.10)
-      parser (>= 3.1.0.0)
+      parser (>= 3.3.0.2)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
-      rexml
-      rubocop-ast (>= 1.16.0, < 2.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
       ruby-progressbar (~> 1.7)
-      unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.16.0)
-      parser (>= 3.1.1.0)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.31.2)
+      parser (>= 3.3.0.4)
     rubocop-rake (0.6.0)
       rubocop (~> 1.0)
     rubocop-rspec (2.9.0)
       rubocop (~> 1.19)
-    ruby-progressbar (1.11.0)
+    ruby-progressbar (1.13.0)
     sqlite3 (1.4.2)
     tzinfo (2.0.4)
       concurrent-ruby (~> 1.0)
-    unicode-display_width (2.1.0)
+    unicode-display_width (2.5.0)
     zeitwerk (2.5.4)
 
 PLATFORMS
diff --git a/lib/parallel.rb b/lib/parallel.rb
index ee83a07..59a72dc 100644
--- a/lib/parallel.rb
+++ b/lib/parallel.rb
@@ -24,7 +24,7 @@ class UndumpableException < StandardError
     attr_reader :backtrace
 
     def initialize(original)
-      super "#{original.class}: #{original.message}"
+      super("#{original.class}: #{original.message}")
       @backtrace = original.backtrace
     end
   end
@@ -300,12 +300,12 @@ def map_with_index(array, options = {}, &block)
       map(array, options.merge(with_index: true), &block)
     end
 
-    def flat_map(*args, &block)
-      map(*args, &block).flatten(1)
+    def flat_map(...)
+      map(...).flatten(1)
     end
 
-    def filter_map(*args, &block)
-      map(*args, &block).compact
+    def filter_map(...)
+      map(...).compact
     end
 
     # Number of physical processor cores on the current system.
@@ -359,7 +359,7 @@ def worker_number=(worker_num)
     private
 
     def add_progress_bar!(job_factory, options)
-      if progress_options = options[:progress]
+      if (progress_options = options[:progress])
         raise "Progressbar can only be used with array like items" if job_factory.size == Float::INFINITY
         require 'ruby-progressbar'
 
@@ -388,7 +388,7 @@ def work_direct(job_factory, options, &block)
       results = []
       exception = nil
       begin
-        while set = job_factory.next
+        while (set = job_factory.next)
           item, index = set
           results << with_instrumentation(item, index, options) do
             call_with_index(item, index, options, &block)
@@ -411,7 +411,7 @@ def work_in_threads(job_factory, options, &block)
       in_threads(options) do |worker_num|
         self.worker_number = worker_num
         # as long as there are more jobs, work on one of them
-        while !exception && set = job_factory.next
+        while !exception && (set = job_factory.next)
           begin
             item, index = set
             result = with_instrumentation item, index, options do
@@ -455,7 +455,7 @@ def work_in_ractors(job_factory, options)
 
       # start
       ractors.dup.each do |ractor|
-        if set = job_factory.next
+        if (set = job_factory.next)
           item, index = set
           instrument_start item, index, options
           ractor.send [callback, item, index]
@@ -466,7 +466,7 @@ def work_in_ractors(job_factory, options)
       end
 
       # replace with new items
-      while set = job_factory.next
+      while (set = job_factory.next)
         item_next, index_next = set
         done, (exception, result, item, index) = Ractor.select(*ractors)
         if exception
@@ -669,7 +669,7 @@ def instrument_finish_in_order(item, index, result, options)
     end
 
     def instrument_start(item, index, options)
-      return unless on_start = options[:start]
+      return unless (on_start = options[:start])
       options[:mutex].synchronize { on_start.call(item, index) }
     end
   end
diff --git a/parallel.gemspec b/parallel.gemspec
index ac77d09..d508190 100644
--- a/parallel.gemspec
+++ b/parallel.gemspec
@@ -16,5 +16,5 @@ Gem::Specification.new name, Parallel::VERSION do |s|
   }
   s.files = `git ls-files lib MIT-LICENSE.txt`.split("\n")
   s.license = "MIT"
-  s.required_ruby_version = '>= 2.5'
+  s.required_ruby_version = '>= 2.7'
 end
diff --git a/spec/cases/each_with_ar_sqlite.rb b/spec/cases/each_with_ar_sqlite.rb
index d326144..fb25dde 100644
--- a/spec/cases/each_with_ar_sqlite.rb
+++ b/spec/cases/each_with_ar_sqlite.rb
@@ -4,7 +4,7 @@
 require "sqlite3"
 require "tempfile"
 $stdout.sync = true
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 
 Tempfile.create("db") do |temp|
   ActiveRecord::Schema.verbose = false
diff --git a/spec/cases/finish_in_order.rb b/spec/cases/finish_in_order.rb
index b8c0339..79e921f 100644
--- a/spec/cases/finish_in_order.rb
+++ b/spec/cases/finish_in_order.rb
@@ -10,7 +10,7 @@ def self.call(item)
 end
 
 method = ENV.fetch('METHOD')
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 $stdout.sync = true
 
 items = [nil, false, 2, 3, 4]
diff --git a/spec/cases/profile_memory.rb b/spec/cases/profile_memory.rb
index 89d13cf..508de4f 100644
--- a/spec/cases/profile_memory.rb
+++ b/spec/cases/profile_memory.rb
@@ -8,7 +8,7 @@ def count_objects
   GC.start
   GC.start
   ObjectSpace.each_object { |o| cur[o.class] += 1 }
-  cur.map { |k, v| [k, v - old[k]] }.to_h.reject { |_k, v| v == 0 }
+  cur.to_h { |k, v| [k, v - old[k]] }.reject { |_k, v| v == 0 }
 end
 
 class Callback
@@ -18,7 +18,7 @@ def self.call(x); end
 require './spec/cases/helper'
 
 items = Array.new(1000)
-options = { "in_#{ARGV[0]}".to_sym => 2 }
+options = { "in_#{ARGV[0]}": 2 }
 
 # TODO: not sure why this fails without 2.times in threading mode :(
 
diff --git a/spec/cases/with_break.rb b/spec/cases/with_break.rb
index 3ea9a27..38bffa5 100644
--- a/spec/cases/with_break.rb
+++ b/spec/cases/with_break.rb
@@ -3,7 +3,7 @@
 $stdout.sync = true # otherwise results can go weird...
 
 method = ENV.fetch('METHOD')
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 worker_size = (ENV['WORKER_SIZE'] || 4).to_i
 
 ARGV.freeze # make ractor happy
diff --git a/spec/cases/with_break_before_finish.rb b/spec/cases/with_break_before_finish.rb
index c5764e7..adfd2e3 100644
--- a/spec/cases/with_break_before_finish.rb
+++ b/spec/cases/with_break_before_finish.rb
@@ -2,7 +2,7 @@
 require './spec/cases/helper'
 
 method = ENV.fetch('METHOD')
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 $stdout.sync = true
 
 class Callback
diff --git a/spec/cases/with_exception.rb b/spec/cases/with_exception.rb
index ffecf53..0b92d0f 100644
--- a/spec/cases/with_exception.rb
+++ b/spec/cases/with_exception.rb
@@ -3,7 +3,7 @@
 $stdout.sync = true # otherwise results can go weird...
 
 method = ENV.fetch('METHOD')
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 worker_size = (ENV['WORKER_SIZE'] || 4).to_i
 
 class ParallelTestError < StandardError
diff --git a/spec/cases/with_exception_before_finish.rb b/spec/cases/with_exception_before_finish.rb
index 5bc429c..d3c876a 100644
--- a/spec/cases/with_exception_before_finish.rb
+++ b/spec/cases/with_exception_before_finish.rb
@@ -2,7 +2,7 @@
 require './spec/cases/helper'
 
 method = ENV.fetch('METHOD')
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 
 class ParallelTestError < StandardError
 end
diff --git a/spec/cases/with_exception_in_finish.rb b/spec/cases/with_exception_in_finish.rb
index 856b791..eecdaae 100644
--- a/spec/cases/with_exception_in_finish.rb
+++ b/spec/cases/with_exception_in_finish.rb
@@ -3,7 +3,7 @@
 
 $stdout.sync = true
 method = ENV.fetch('METHOD')
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 
 class ParallelTestError < StandardError
 end
diff --git a/spec/cases/with_exception_in_start.rb b/spec/cases/with_exception_in_start.rb
index 6d49117..e409df3 100644
--- a/spec/cases/with_exception_in_start.rb
+++ b/spec/cases/with_exception_in_start.rb
@@ -2,7 +2,7 @@
 require './spec/cases/helper'
 
 method = ENV.fetch('METHOD')
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 
 class ParallelTestError < StandardError
 end
diff --git a/spec/cases/with_exception_in_start_before_finish.rb b/spec/cases/with_exception_in_start_before_finish.rb
index 7ff5a05..472cfb1 100644
--- a/spec/cases/with_exception_in_start_before_finish.rb
+++ b/spec/cases/with_exception_in_start_before_finish.rb
@@ -2,7 +2,7 @@
 require './spec/cases/helper'
 
 method = ENV.fetch('METHOD')
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 $stdout.sync = true
 
 class ParallelTestError < StandardError
diff --git a/spec/cases/with_worker_number.rb b/spec/cases/with_worker_number.rb
index 6afaab5..8a9976e 100644
--- a/spec/cases/with_worker_number.rb
+++ b/spec/cases/with_worker_number.rb
@@ -2,7 +2,7 @@
 require './spec/cases/helper'
 
 method = ENV.fetch('METHOD')
-in_worker_type = "in_#{ENV.fetch('WORKER_TYPE')}".to_sym
+in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 
 Parallel.public_send(method, 1..100, in_worker_type => 4) do
   sleep 0.1 # so all workers get started
diff --git a/spec/parallel_spec.rb b/spec/parallel_spec.rb
index e445898..39e2598 100644
--- a/spec/parallel_spec.rb
+++ b/spec/parallel_spec.rb
@@ -144,7 +144,7 @@ def cpus
         kill_process_with_name("spec/cases/parallel_fast_exit.rb") # simulates Ctrl+c
         sleep 1
         result = t.value
-        result.scan(/I finished/).size.should == 3
+        result.scan("I finished").size.should == 3
         result.should_not include("Parallel execution interrupted")
       end.should <= 4
     end
@@ -334,7 +334,7 @@ def cpus
 
       it "sets Parallel.worker_number with 0 #{type}" do
         skip if type == "ractors" # not supported
-        type_key = "in_#{type}".to_sym
+        type_key = :"in_#{type}"
         result = Parallel.map([1, 2, 3, 4, 5, 6, 7, 8, 9], type_key => 0) { |_x| Parallel.worker_number }
         result.uniq.should == [0]
         Parallel.worker_number.should be_nil
@@ -343,7 +343,7 @@ def cpus
       it "can run with 0 by not using #{type}" do
         Thread.should_not_receive(:exclusive)
         Process.should_not_receive(:fork)
-        result = Parallel.map([1, 2, 3, 4, 5, 6, 7, 8, 9], "in_#{type}".to_sym => 0) { |x| x + 2 }
+        result = Parallel.map([1, 2, 3, 4, 5, 6, 7, 8, 9], "in_#{type}": 0) { |x| x + 2 }
         result.should == [3, 4, 5, 6, 7, 8, 9, 10, 11]
       end