diff --git a/core/struct/keyword_init_spec.rb b/core/struct/keyword_init_spec.rb
new file mode 100644
index 0000000000..e5e066f42e
--- /dev/null
+++ b/core/struct/keyword_init_spec.rb
@@ -0,0 +1,20 @@
+require_relative '../../spec_helper'
+
+describe "Struct#keyword_init?" do
+  ruby_version_is '3.1' do # https://bugs.ruby-lang.org/issues/18008
+    it "returns true if it's initialized with keyword_init: true option" do
+      klass = Struct.new(:name, keyword_init: true)
+      klass.keyword_init?.should == true
+    end
+
+    it "returns false if it's initialized with keyword_init: false option" do
+      klass = Struct.new(:name, keyword_init: false)
+      klass.keyword_init?.should == false
+    end
+
+    it "returns nil if it's initialized without keyword_init option" do
+      klass = Struct.new(:name)
+      klass.keyword_init?.should == nil
+    end
+  end
+end