diff --git a/Gemfile b/Gemfile
index 708bbac..896d547 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,4 +1,3 @@
 source "https://rubygems.org"
 
-gemspec
-gem 'concurrent-ruby'
\ No newline at end of file
+gemspec
\ No newline at end of file
diff --git a/lib/wayback_machine_downloader.rb b/lib/wayback_machine_downloader.rb
index c7d2e2d..c54834b 100644
--- a/lib/wayback_machine_downloader.rb
+++ b/lib/wayback_machine_downloader.rb
@@ -7,7 +7,7 @@ require 'fileutils'
 require 'cgi'
 require 'json'
 require 'time'
-require 'concurrent'
+require 'concurrent-ruby'
 require 'logger'
 require_relative 'wayback_machine_downloader/tidy_bytes'
 require_relative 'wayback_machine_downloader/to_regex'
diff --git a/wayback_machine_downloader.gemspec b/wayback_machine_downloader.gemspec
index 10139fe..60797f1 100644
--- a/wayback_machine_downloader.gemspec
+++ b/wayback_machine_downloader.gemspec
@@ -1,3 +1,5 @@
+require './lib/wayback_machine_downloader'
+
 Gem::Specification.new do |s|
   s.name        = "wayback_machine_downloader"
   s.version     = WaybackMachineDownloader::VERSION
@@ -10,7 +12,7 @@ Gem::Specification.new do |s|
   s.homepage    = "https://github.com/hartator/wayback-machine-downloader"
   s.license     = "MIT"
   s.required_ruby_version = '>= 1.9.2'
-  s.add_runtime_dependency 'concurrent-ruby', '~> 1.2'
+  s.add_runtime_dependency 'concurrent-ruby', '~> 1.3', '>= 1.3.4'
   s.add_development_dependency 'rake', '~> 12.2'
   s.add_development_dependency 'minitest', '~> 5.2'
 end