diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d889dd7..bc8cc4e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -12,7 +12,7 @@ on:
       - 'Gemfile.lock'
     branches:
       - master
-      - gh_workflows
+      - drop_compat
 
   pull_request:
     paths:
@@ -36,11 +36,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [1.9.3, 2.1, 2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1]
+        ruby: [2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, 3.3]
         experimental: [false]
         include:
-          - ruby: '2.0'
-            experimental: true
           - ruby: jruby-head
             experimental: true
           - ruby: truffleruby-head
diff --git a/Gemfile b/Gemfile
index 838a0f6..bc03aa0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,14 +1,13 @@
-source "https://rubygems.org"
+source 'https://rubygems.org'
 
-gem "rspec", "~> 3.4.0"
-gem "rake", "~> 10.3.0"
-gem "pry", "~> 0.11.0"
-gem "pry-doc", "~> 0.9.0", require: false, platforms: :mri
-gem "method_source", ">= 0.8.2"
+gem 'rspec', '~> 3.4.0'
+gem 'rake', '~> 13.1'
+gem 'pry', '~> 0.11.0'
+gem 'pry-doc', '~> 0.9.0', require: false, platforms: :mri
+gem 'method_source', '>= 0.8.2'
 gem 'activesupport', '~> 4.1.11'
 gem 'yard', '~> 0.9.11'
-gem 'minitest', '~> 5.11.3' # Because we still like Ruby 1.9.3
 
 group :metrics do
-  gem "simplecov", require: false
+  gem 'simplecov', require: false
 end
diff --git a/Gemfile.lock b/Gemfile.lock
index b19ea1b..e18c8c1 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -10,7 +10,7 @@ GEM
     coderay (1.1.3)
     concurrent-ruby (1.1.6)
     diff-lcs (1.3)
-    ffi (1.12.2-java)
+    ffi (1.15.5-java)
     i18n (0.9.5)
       concurrent-ruby (~> 1.0)
     json (1.8.6)
@@ -28,7 +28,7 @@ GEM
     pry-doc (0.9.0)
       pry (~> 0.9)
       yard (~> 0.8)
-    rake (10.3.0)
+    rake (13.1.0)
     rspec (3.4.0)
       rspec-core (~> 3.4.0)
       rspec-expectations (~> 3.4.0)
@@ -64,10 +64,10 @@ DEPENDENCIES
   minitest (~> 5.11.3)
   pry (~> 0.11.0)
   pry-doc (~> 0.9.0)
-  rake (~> 10.3.0)
+  rake (~> 13.1)
   rspec (~> 3.4.0)
   simplecov
   yard (~> 0.9.11)
 
 BUNDLED WITH
-   1.17.3
+   2.3.27
diff --git a/spec/robe/jvisor_spec.rb b/spec/robe/jvisor_spec.rb
index 0963cc9..ef8cc25 100644
--- a/spec/robe/jvisor_spec.rb
+++ b/spec/robe/jvisor_spec.rb
@@ -1,5 +1,6 @@
 require 'spec_helper'
 require 'robe/jvisor'
+require 'set'
 
 describe Robe::JVisor do
   subject { Robe::JVisor.new }