diff --git a/lib/json.rb b/lib/json.rb
index 61bb8fae0e..8132cd571c 100644
--- a/lib/json.rb
+++ b/lib/json.rb
@@ -55,9 +55,5 @@ require 'json/common'
 module JSON
   require 'json/version'
 
-  begin
-    require 'json/ext'
-  rescue LoadError
-    require 'json/pure'
-  end
+  require 'json/pure'
 end
diff --git a/tests/setup_variant.rb b/tests/setup_variant.rb
index f7fb2a1d56..5e9e050a26 100644
--- a/tests/setup_variant.rb
+++ b/tests/setup_variant.rb
@@ -1,12 +1,3 @@
 # frozen_string_literal: false
-case ENV['JSON']
-when 'pure'
-  $:.unshift 'lib'
-  require 'json/pure'
-when 'ext'
-  $:.unshift 'ext', 'lib'
-  require 'json/ext'
-else
-  $:.unshift 'ext', 'lib'
-  require 'json'
-end
+$:.unshift 'lib'
+require 'json'
diff --git a/tests/test_json.rb b/tests/test_json.rb
index 8fe9459978..b81ee506af 100755
--- a/tests/test_json.rb
+++ b/tests/test_json.rb
@@ -537,15 +537,6 @@ EOT
     assert_equal orig, JSON[json5][0]
   end
 
-  if defined?(JSON::Ext::Parser)
-    def test_allocate
-      parser = JSON::Ext::Parser.new("{}")
-      assert_raise(TypeError, '[ruby-core:35079]') {parser.__send__(:initialize, "{}")}
-      parser = JSON::Ext::Parser.allocate
-      assert_raise(TypeError, '[ruby-core:35079]') {parser.source}
-    end
-  end
-
   def test_argument_encoding
     source = "{}".force_encoding("ascii-8bit")
     JSON::Parser.new(source)
@@ -565,13 +556,13 @@ EOT
   if EnvUtil.gc_stress_to_class?
     def assert_no_memory_leak(code, *rest, **opt)
       code = "8.times {20_000.times {begin #{code}; rescue NoMemoryError; end}; GC.start}"
-      super(["-rjson/ext/parser"],
-            "GC.add_stress_to_class(JSON::Ext::Parser); "\
+      super(["-rjson/pure/parser"],
+            "GC.add_stress_to_class(JSON::Pure::Parser); "\
             "#{code}", code, *rest, rss: true, limit: 1.1, **opt)
     end
 
     def test_no_memory_leak_allocate
-      assert_no_memory_leak("JSON::Ext::Parser.allocate")
+      assert_no_memory_leak("JSON::Pure::Parser.allocate")
     end
   end
 end
diff --git a/tests/test_json_generate.rb b/tests/test_json_generate.rb
index 50895f6247..f85dd3a81c 100755
--- a/tests/test_json_generate.rb
+++ b/tests/test_json_generate.rb
@@ -283,28 +283,6 @@ EOT
     assert_equal '2', state.indent
   end
 
-  if defined?(JSON::Ext::Generator)
-    def test_broken_bignum # [ruby-core:38867]
-      pid = fork do
-        Bignum.class_eval do
-          def to_s
-          end
-        end
-        begin
-          JSON::Ext::Generator::State.new.generate(1<<64)
-          exit 1
-        rescue TypeError
-          exit 0
-        end
-      end
-      _, status = Process.waitpid2(pid)
-      assert status.success?
-    rescue NotImplementedError
-      # forking to avoid modifying core class of a parent process and
-      # introducing race conditions of tests are run in parallel
-    end
-  end
-
   def test_hash_likeness_set_symbol
     state = JSON.state.new
     assert_equal nil, state[:foo]
@@ -349,13 +327,13 @@ EOT
   if EnvUtil.gc_stress_to_class?
     def assert_no_memory_leak(code, *rest, **opt)
       code = "8.times {20_000.times {begin #{code}; rescue NoMemoryError; end}; GC.start}"
-      super(["-rjson/ext/generator"],
-            "GC.add_stress_to_class(JSON::Ext::Generator::State); "\
+      super(["-rjson/pure/generator"],
+            "GC.add_stress_to_class(JSON::Pure::Generator::State); "\
             "#{code}", code, *rest, rss: true, limit: 1.1, **opt)
     end
 
     def test_no_memory_leak_allocate
-      assert_no_memory_leak("JSON::Ext::Generator::State.allocate")
+      assert_no_memory_leak("JSON::Pure::Generator::State.allocate")
     end
   end
 end