diff --git a/language/fixtures/variables.rb b/language/fixtures/variables.rb
index 527caa7a7..3c9271edc 100644
--- a/language/fixtures/variables.rb
+++ b/language/fixtures/variables.rb
@@ -154,4 +154,46 @@ class Node
       attr_accessor :left, :right
     end
   end
+
+  module RactorAccess
+    singleton_class.attr_accessor :ivar
+
+    class << self
+      def run(code_str)
+        require_path = File.expand_path(__FILE__)
+
+        code = <<~RUBY
+          require_relative "#{require_path}"
+
+          puts #{code_str}
+        RUBY
+
+        ruby_exe(code).chomp
+      end
+
+      def read_in_ractor(shareable = true)
+        run_in_ractor(shareable, :read)
+      end
+
+      def write_in_ractor(shareable = true)
+        run_in_ractor(shareable, :write)
+      end
+
+      def run_in_ractor(shareable, type)
+        @ivar = shareable ? 3 : "3"
+
+        r = Ractor.new(type) do |type|
+          if type == :read
+            RactorAccess.ivar
+          else
+            RactorAccess.ivar = 4
+          end
+        rescue => e
+          e.class.name
+        end
+
+        r.take
+      end
+    end
+  end
 end
diff --git a/language/variables_spec.rb b/language/variables_spec.rb
index 23c2cdb55..771353761 100644
--- a/language/variables_spec.rb
+++ b/language/variables_spec.rb
@@ -937,3 +937,58 @@ def obj.foobar; $specs_uninitialized_global_variable_lazy ||= 42; end
     end
   end
 end
+
+describe "Module instance variables within Ractors" do
+  context "when the instance variable is shareable" do
+    ruby_version_is ""..."3.1" do
+      it "raises Isolation error if read from a non-main Ractor" do
+        result = VariablesSpecs::RactorAccess.run("VariablesSpecs::RactorAccess.read_in_ractor")
+        result.should == "Ractor::IsolationError"
+      end
+    end
+
+    ruby_version_is "3.1" do
+      it "can be read from a non-main Ractor" do
+        result = VariablesSpecs::RactorAccess.run("VariablesSpecs::RactorAccess.read_in_ractor")
+        result.should == "3"
+      end
+    end
+
+    it "raises Isolation error if written to in a non-main Ractor" do
+      result = VariablesSpecs::RactorAccess.run("VariablesSpecs::RactorAccess.write_in_ractor")
+      result.should == "Ractor::IsolationError"
+    end
+
+    it "raises no error if read/written in the main Ractor" do
+      code = <<~RUBY
+        VariablesSpecs::RactorAccess.ivar = 5
+        VariablesSpecs::RactorAccess.ivar
+      RUBY
+
+      result = VariablesSpecs::RactorAccess.run(code)
+      result.should == "5"
+    end
+  end
+
+  context "when the instance variable is not shareable" do
+    it "raises Isolation error if read from a non-main Ractor" do
+        result = VariablesSpecs::RactorAccess.run("VariablesSpecs::RactorAccess.read_in_ractor(false)")
+        result.should == "Ractor::IsolationError"
+    end
+
+    it "raises Isolation error if written to in a non-main Ractor" do
+      result = VariablesSpecs::RactorAccess.run("VariablesSpecs::RactorAccess.write_in_ractor(false)")
+      result.should == "Ractor::IsolationError"
+    end
+
+    it "raises no error if read/written in the main Ractor" do
+      code = <<~RUBY
+        VariablesSpecs::RactorAccess.ivar = 5
+        VariablesSpecs::RactorAccess.ivar
+      RUBY
+
+      result = VariablesSpecs::RactorAccess.run(code)
+      result.should == "5"
+    end
+  end
+end