diff --git a/Gemfile.lock b/Gemfile.lock
index a610966d..4d3f3993 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    mutant (0.8.18)
+    mutant (0.8.19)
       abstract_type (~> 0.0.7)
       adamantium (~> 0.2.0)
       anima (~> 0.3.0)
@@ -12,13 +12,12 @@ PATH
       ice_nine (~> 0.11.1)
       memoizable (~> 0.4.2)
       morpher (~> 0.2.6)
-      parallel (~> 1.3)
       parser (~> 2.5.1)
       procto (~> 0.0.2)
       regexp_parser (~> 1.2)
       unparser (~> 0.2.5)
-    mutant-rspec (0.8.18)
-      mutant (~> 0.8.18)
+    mutant-rspec (0.8.19)
+      mutant (~> 0.8.19)
       rspec-core (>= 3.4.0, < 4.0.0)
 
 GEM
@@ -168,6 +167,7 @@ DEPENDENCIES
   devtools (~> 0.1.21)
   ffi (~> 1.9.6)
   mutant!
+  parallel (~> 1.3)
 
 BUNDLED WITH
    1.17.1
diff --git a/lib/mutant.rb b/lib/mutant.rb
index d7b9708b..2bbefeaf 100644
--- a/lib/mutant.rb
+++ b/lib/mutant.rb
@@ -4,15 +4,15 @@ require 'abstract_type'
 require 'adamantium'
 require 'anima'
 require 'concord'
-require 'digest/sha1'
 require 'diff/lcs'
 require 'diff/lcs/hunk'
+require 'digest/sha1'
+require 'etc'
 require 'equalizer'
 require 'ice_nine'
 require 'morpher'
 require 'open3'
 require 'optparse'
-require 'parallel'
 require 'parser'
 require 'parser/current'
 require 'pathname'
@@ -228,7 +228,7 @@ module Mutant
         marshal: Marshal,
         process: Process
       ),
-      jobs:              ::Parallel.processor_count,
+      jobs:              Etc.nprocessors,
       kernel:            Kernel,
       load_path:         $LOAD_PATH,
       matcher:           Matcher::Config::DEFAULT,
diff --git a/mutant.gemspec b/mutant.gemspec
index 716b0fb2..2be151a2 100644
--- a/mutant.gemspec
+++ b/mutant.gemspec
@@ -33,7 +33,6 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency('ice_nine',      '~> 0.11.1')
   gem.add_runtime_dependency('memoizable',    '~> 0.4.2')
   gem.add_runtime_dependency('morpher',       '~> 0.2.6')
-  gem.add_runtime_dependency('parallel',      '~> 1.3')
   gem.add_runtime_dependency('parser',        '~> 2.5.1')
   gem.add_runtime_dependency('procto',        '~> 0.0.2')
   gem.add_runtime_dependency('regexp_parser', '~> 1.2')
@@ -42,4 +41,5 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency('bundler',  '~> 1.10')
   gem.add_development_dependency('devtools', '~> 0.1.21')
   gem.add_development_dependency('ffi',      '~> 1.9.6')
+  gem.add_development_dependency('parallel', '~> 1.3')
 end
diff --git a/spec/support/corpus.rb b/spec/support/corpus.rb
index 8b31c39b..1c2aa7c6 100644
--- a/spec/support/corpus.rb
+++ b/spec/support/corpus.rb
@@ -1,8 +1,9 @@
 # frozen_string_literal: true
 
-require 'morpher'
 require 'anima'
+require 'morpher'
 require 'mutant'
+require 'parallel'
 
 # @api private
 module MutantSpec
@@ -188,7 +189,7 @@ module MutantSpec
         if ENV.key?('CI')
           CIRCLE_CI_CONTAINER_PROCESSES
         else
-          Parallel.processor_count
+          Etc.nprocessors
         end
       end