diff --git a/.rubocop.yml b/.rubocop.yml
index 3323c741..4dbeeb33 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -13,6 +13,9 @@ AllCops:
 Layout/LineLength:
   Max: 80
 
+Lint/AmbiguousBlockAssociation:
+  Enabled: false
+
 Lint/DuplicateBranch:
   Enabled: false
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c4558185..dc5dc7d5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,14 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 
 ## [Unreleased]
 
+## [4.0.1] - 2022-10-18
+
+### Changed
+
+- [#172](https://github.com/ruby-syntax-tree/syntax_tree/pull/172) - Use a refinement for `Symbol#name` addition so that other runtimes or tools don't get confused by its availability.
+- [#173](https://github.com/ruby-syntax-tree/syntax_tree/pull/173) - Fix the `current_environment` usage to use the method instead of the instance variable.
+- [#175](https://github.com/ruby-syntax-tree/syntax_tree/pull/175) - Update `prettier_print` requirement since v1.0.0 had a bug with `#breakable_return`.
+
 ## [4.0.0] - 2022-10-17
 
 ### Added
diff --git a/Gemfile.lock b/Gemfile.lock
index 00ae409b..f55c7768 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,8 +1,8 @@
 PATH
   remote: .
   specs:
-    syntax_tree (4.0.0)
-      prettier_print (>= 1.0.0)
+    syntax_tree (4.0.1)
+      prettier_print (>= 1.0.1)
 
 GEM
   remote: https://rubygems.org/
@@ -14,7 +14,7 @@ GEM
     parallel (1.22.1)
     parser (3.1.2.1)
       ast (~> 2.4.1)
-    prettier_print (1.0.0)
+    prettier_print (1.0.1)
     rainbow (3.1.1)
     rake (13.0.6)
     regexp_parser (2.6.0)
@@ -29,7 +29,7 @@ GEM
       rubocop-ast (>= 1.20.1, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.21.0)
+    rubocop-ast (1.22.0)
       parser (>= 3.1.1.0)
     ruby-progressbar (1.11.0)
     simplecov (0.21.2)
diff --git a/lib/syntax_tree.rb b/lib/syntax_tree.rb
index 52ec700b..fbd4fcef 100644
--- a/lib/syntax_tree.rb
+++ b/lib/syntax_tree.rb
@@ -22,16 +22,6 @@
 
 require_relative "syntax_tree/parser"
 
-# We rely on Symbol#name being available, which is only available in Ruby 3.0+.
-# In case we're running on an older Ruby version, we polyfill it here.
-unless :+.respond_to?(:name)
-  class Symbol # rubocop:disable Style/Documentation
-    def name
-      to_s.freeze
-    end
-  end
-end
-
 # Syntax Tree is a suite of tools built on top of the internal CRuby parser. It
 # provides the ability to generate a syntax tree from source, as well as the
 # tools necessary to inspect and manipulate that syntax tree. It can be used to
diff --git a/lib/syntax_tree/node.rb b/lib/syntax_tree/node.rb
index dcdd0275..5162655e 100644
--- a/lib/syntax_tree/node.rb
+++ b/lib/syntax_tree/node.rb
@@ -1651,6 +1651,20 @@ def format(q)
   #     array << value
   #
   class Binary < Node
+    # Since Binary's operator is a symbol, it's better to use the `name` method
+    # than to allocate a new string every time. This is a tiny performance
+    # optimization, but enough that it shows up in the profiler. Adding this in
+    # for older Ruby versions.
+    unless :+.respond_to?(:name)
+      using Module.new {
+        refine Symbol do
+          def name
+            to_s.freeze
+          end
+        end
+      }
+    end
+
     # [untyped] the left-hand side of the expression
     attr_reader :left
 
diff --git a/lib/syntax_tree/version.rb b/lib/syntax_tree/version.rb
index 8456abd4..695f4c88 100644
--- a/lib/syntax_tree/version.rb
+++ b/lib/syntax_tree/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module SyntaxTree
-  VERSION = "4.0.0"
+  VERSION = "4.0.1"
 end
diff --git a/lib/syntax_tree/visitor/with_environment.rb b/lib/syntax_tree/visitor/with_environment.rb
index 62e59c98..ad101e0a 100644
--- a/lib/syntax_tree/visitor/with_environment.rb
+++ b/lib/syntax_tree/visitor/with_environment.rb
@@ -64,19 +64,19 @@ def visit_def_endless(node)
     # arguments
     def visit_params(node)
       node.requireds.each do |param|
-        @current_environment.add_local_definition(param, :argument)
+        current_environment.add_local_definition(param, :argument)
       end
 
       node.posts.each do |param|
-        @current_environment.add_local_definition(param, :argument)
+        current_environment.add_local_definition(param, :argument)
       end
 
       node.keywords.each do |param|
-        @current_environment.add_local_definition(param.first, :argument)
+        current_environment.add_local_definition(param.first, :argument)
       end
 
       node.optionals.each do |param|
-        @current_environment.add_local_definition(param.first, :argument)
+        current_environment.add_local_definition(param.first, :argument)
       end
 
       super
@@ -84,21 +84,21 @@ def visit_params(node)
 
     def visit_rest_param(node)
       name = node.name
-      @current_environment.add_local_definition(name, :argument) if name
+      current_environment.add_local_definition(name, :argument) if name
 
       super
     end
 
     def visit_kwrest_param(node)
       name = node.name
-      @current_environment.add_local_definition(name, :argument) if name
+      current_environment.add_local_definition(name, :argument) if name
 
       super
     end
 
     def visit_blockarg(node)
       name = node.name
-      @current_environment.add_local_definition(name, :argument) if name
+      current_environment.add_local_definition(name, :argument) if name
 
       super
     end
@@ -108,7 +108,7 @@ def visit_var_field(node)
       value = node.value
 
       if value.is_a?(SyntaxTree::Ident)
-        @current_environment.add_local_definition(value, :variable)
+        current_environment.add_local_definition(value, :variable)
       end
 
       super
@@ -119,7 +119,7 @@ def visit_var_field(node)
     # Visits for keeping track of variable and argument usages
     def visit_aref_field(node)
       name = node.collection.value
-      @current_environment.add_local_usage(name, :variable) if name
+      current_environment.add_local_usage(name, :variable) if name
 
       super
     end
@@ -128,10 +128,10 @@ def visit_var_ref(node)
       value = node.value
 
       if value.is_a?(SyntaxTree::Ident)
-        definition = @current_environment.find_local(value.value)
+        definition = current_environment.find_local(value.value)
 
         if definition
-          @current_environment.add_local_usage(value, definition.type)
+          current_environment.add_local_usage(value, definition.type)
         end
       end
 
diff --git a/syntax_tree.gemspec b/syntax_tree.gemspec
index ec7d57ef..fe74c7e7 100644
--- a/syntax_tree.gemspec
+++ b/syntax_tree.gemspec
@@ -25,7 +25,7 @@ Gem::Specification.new do |spec|
   spec.executables = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = %w[lib]
 
-  spec.add_dependency "prettier_print", ">= 1.0.0"
+  spec.add_dependency "prettier_print", ">= 1.0.1"
 
   spec.add_development_dependency "bundler"
   spec.add_development_dependency "minitest"
diff --git a/test/visitor_with_environment_test.rb b/test/visitor_with_environment_test.rb
index 915b2143..302dbfbe 100644
--- a/test/visitor_with_environment_test.rb
+++ b/test/visitor_with_environment_test.rb
@@ -406,5 +406,25 @@ def foo(a)
       assert_equal(2, argument.usages[0].start_line)
       assert_equal(4, argument.usages[1].start_line)
     end
+
+    def test_variables_in_the_top_level
+      tree = SyntaxTree.parse(<<~RUBY)
+        a = 123
+        a
+      RUBY
+
+      visitor = Collector.new
+      visitor.visit(tree)
+
+      assert_equal(0, visitor.arguments.length)
+      assert_equal(1, visitor.variables.length)
+
+      variable = visitor.variables["a"]
+      assert_equal(1, variable.definitions.length)
+      assert_equal(1, variable.usages.length)
+
+      assert_equal(1, variable.definitions[0].start_line)
+      assert_equal(2, variable.usages[0].start_line)
+    end
   end
 end