diff --git a/core/kernel/warn_spec.rb b/core/kernel/warn_spec.rb
index 79e78dd4a3..de08cd8cff 100644
--- a/core/kernel/warn_spec.rb
+++ b/core/kernel/warn_spec.rb
@@ -17,7 +17,7 @@
     Kernel.should have_private_instance_method(:warn)
   end
 
-  it "requires multiple arguments" do
+  it "accepts multiple arguments" do
     Kernel.method(:warn).arity.should < 0
   end
 
@@ -114,6 +114,38 @@
       end
     end
 
+    ruby_version_is "3.0" do
+      it "accepts :category keyword with a symbol" do
+        -> {
+          $VERBOSE = true
+          warn("message", category: :deprecated)
+        }.should output(nil, "message\n")
+      end
+
+      it "accepts :category keyword with nil" do
+        -> {
+          $VERBOSE = true
+          warn("message", category: nil)
+        }.should output(nil, "message\n")
+      end
+
+      it "accepts :category keyword with object convertible to symbol" do
+        o = Object.new
+        def o.to_sym; :deprecated; end
+        -> {
+          $VERBOSE = true
+          warn("message", category: o)
+        }.should output(nil, "message\n")
+      end
+
+      it "raises if :category keyword is not nil and not convertible to symbol" do
+        -> {
+          $VERBOSE = true
+          warn("message", category: Object.new)
+        }.should raise_error(TypeError)
+      end
+    end
+
     it "converts first arg using to_s" do
       w = KernelSpecs::WarnInNestedCall.new
 
diff --git a/core/warning/warn_spec.rb b/core/warning/warn_spec.rb
index 21424c6c76..2ded6a109d 100644
--- a/core/warning/warn_spec.rb
+++ b/core/warning/warn_spec.rb
@@ -51,14 +51,41 @@ def Warning.warn(msg)
     end
   end
 
-  it "is called by Kernel.warn" do
-    Warning.should_receive(:warn).with("Chunky bacon!\n")
-    verbose = $VERBOSE
-    $VERBOSE = false
-    begin
-      Kernel.warn("Chunky bacon!")
-    ensure
-      $VERBOSE = verbose
+
+  ruby_version_is '3.0' do
+    it "is called by Kernel.warn with nil category keyword" do
+      Warning.should_receive(:warn).with("Chunky bacon!\n", category: nil)
+      verbose = $VERBOSE
+      $VERBOSE = false
+      begin
+        Kernel.warn("Chunky bacon!")
+      ensure
+        $VERBOSE = verbose
+      end
+    end
+
+    it "is called by Kernel.warn with given category keyword converted to a symbol" do
+      Warning.should_receive(:warn).with("Chunky bacon!\n", category: :deprecated)
+      verbose = $VERBOSE
+      $VERBOSE = false
+      begin
+        Kernel.warn("Chunky bacon!", category: 'deprecated')
+      ensure
+        $VERBOSE = verbose
+      end
+    end
+  end
+
+  ruby_version_is ''...'3.0' do
+    it "is called by Kernel.warn" do
+      Warning.should_receive(:warn).with("Chunky bacon!\n")
+      verbose = $VERBOSE
+      $VERBOSE = false
+      begin
+        Kernel.warn("Chunky bacon!")
+      ensure
+        $VERBOSE = verbose
+      end
     end
   end
 end