diff --git a/ext/io/event/selector/uring.c b/ext/io/event/selector/uring.c
index a0e4e810..ab0e40ff 100644
--- a/ext/io/event/selector/uring.c
+++ b/ext/io/event/selector/uring.c
@@ -997,14 +997,13 @@ VALUE IO_Event_Selector_URing_io_pwrite(VALUE self, VALUE fiber, VALUE io, VALUE
 
 static const int ASYNC_CLOSE = 1;
 
-VALUE IO_Event_Selector_URing_io_close(VALUE self, VALUE io) {
+VALUE IO_Event_Selector_URing_io_close(VALUE self, VALUE _descriptor) {
 	struct IO_Event_Selector_URing *selector = NULL;
 	TypedData_Get_Struct(self, struct IO_Event_Selector_URing, &IO_Event_Selector_URing_Type, selector);
 	
-	// Ruby's fiber scheduler io_close hook may receive a raw Integer fd
-	// (observed on Ruby head/4.1) rather than an IO object.
-	int descriptor = RB_INTEGER_TYPE_P(io) ? RB_NUM2INT(io) : IO_Event_Selector_io_descriptor(io);
-
+	// Ruby's fiber scheduler `io_close` hook is invoked with a raw integer file descriptor (Ruby 4.0+); it does not pass the `IO` object.
+	int descriptor = RB_NUM2INT(_descriptor);
+	
 	if (ASYNC_CLOSE) {
 		struct io_uring_sqe *sqe = io_get_sqe(selector);
 		io_uring_prep_close(sqe, descriptor);
@@ -1017,8 +1016,8 @@ VALUE IO_Event_Selector_URing_io_close(VALUE self, VALUE io) {
 	} else {
 		close(descriptor);
 	}
-
-	// We don't wait for the result of close since it has no use in pratice:
+	
+	// We don't wait for the result of close since it has no use in practice:
 	return Qtrue;
 }
 
diff --git a/fixtures/io/event/test_scheduler.rb b/fixtures/io/event/test_scheduler.rb
index 7faed994..f605b1b3 100644
--- a/fixtures/io/event/test_scheduler.rb
+++ b/fixtures/io/event/test_scheduler.rb
@@ -30,6 +30,14 @@ module IO::Event
 	# end.resume
 	# ```
 	class TestScheduler
+		# Optional fiber scheduler hooks that we forward to the underlying selector. Mixed into the scheduler's singleton class only when the selector actually implements the corresponding method, so feature detection via `respond_to?` reflects the real backend (and Ruby falls back to its default behaviour otherwise).
+		module Forwarders
+			# Fiber scheduler hook for `IO#close`. Ruby invokes this with a raw integer file descriptor (Ruby 4.0+).
+			def io_close(descriptor)
+				@selector.io_close(descriptor)
+			end
+		end
+		
 		def initialize(selector: nil, worker_pool: nil, maximum_worker_count: nil)
 			@selector = selector || ::IO::Event::Selector.new(Fiber.current)
 			
@@ -42,6 +50,20 @@ def initialize(selector: nil, worker_pool: nil, maximum_worker_count: nil)
 			# Track the number of fibers that are blocked.
 			@blocked = 0
 			@blocking = {}
+			
+			install_optional_forwarders(@selector)
+		end
+		
+		private def install_optional_forwarders(selector)
+			forwarders = nil
+			
+			Forwarders.instance_methods(false).each do |name|
+				next unless selector.respond_to?(name)
+				forwarders ||= Module.new
+				forwarders.define_method(name, Forwarders.instance_method(name))
+			end
+			
+			singleton_class.include(forwarders) if forwarders
 		end
 		
 		# @attribute [WorkerPool] The worker pool used for executing blocking operations.
diff --git a/lib/io/event/debug/selector.rb b/lib/io/event/debug/selector.rb
index d087ed69..b611d861 100644
--- a/lib/io/event/debug/selector.rb
+++ b/lib/io/event/debug/selector.rb
@@ -10,6 +10,17 @@ module Debug
 		#
 		# You can enable this in the default selector by setting the `IO_EVENT_DEBUG_SELECTOR` environment variable. In addition, you can log all selector operations to a file by setting the `IO_EVENT_DEBUG_SELECTOR_LOG` environment variable. This is useful for debugging and understanding the behavior of the event loop.
 		class Selector
+			# Forwarders for optional selector hooks that not every backing selector implements (e.g. `io_close` is only provided by `URing`). Each method here is mixed into the wrapper's singleton class only when the wrapped selector actually defines a method of the same name, so feature detection via `respond_to?` continues to reflect the real backend.
+			module Forwarders
+				# Close a file descriptor, forwarded to the underlying selector. Ruby invokes this hook with a raw integer descriptor (Ruby 4.0+).
+				#
+				# @parameter descriptor [Integer] The raw file descriptor being closed.
+				def io_close(descriptor)
+					log("Closing file descriptor #{descriptor}")
+					@selector.io_close(descriptor)
+				end
+			end
+			
 			# Wrap the given selector with debugging.
 			#
 			# @parameter selector [Selector] The selector to wrap.
@@ -40,6 +51,20 @@ def initialize(selector, log: nil)
 				end
 				
 				@log = log
+				
+				install_optional_forwarders(selector)
+			end
+			
+			private def install_optional_forwarders(selector)
+				forwarders = nil
+				
+				Forwarders.instance_methods(false).each do |name|
+					next unless selector.class.method_defined?(name)
+					forwarders ||= Module.new
+					forwarders.define_method(name, Forwarders.instance_method(name))
+				end
+				
+				singleton_class.include(forwarders) if forwarders
 			end
 			
 			# The idle duration of the underlying selector.
diff --git a/test/io/event/selector/io_close.rb b/test/io/event/selector/io_close.rb
index 873a3ea9..e5b9daac 100644
--- a/test/io/event/selector/io_close.rb
+++ b/test/io/event/selector/io_close.rb
@@ -5,37 +5,21 @@
 
 require "io/event"
 require "io/event/selector"
+require "io/event/debug/selector"
 
+# Ruby invokes the `io_close` fiber-scheduler hook with a raw integer file descriptor (Ruby 4.0+, see `rb_fiber_scheduler_io_close` in CRuby). Verify each selector that opts into the hook handles that contract.
 IOClose = Sus::Shared("io_close") do
-	it "can close an IO object" do
+	it "can close a raw file descriptor" do
 		selector = subject.new(Fiber.current)
-		next unless selector.respond_to?(:io_close)
 		
 		input, output = IO.pipe
 		
-		begin
-			expect(selector.io_close(input)).to be_truthy
-		ensure
-			input.close rescue nil
-			output.close rescue nil
-			selector.close
-		end
-	end
-	
-	# Ruby head/4.1 passes a raw Integer fd to the io_close scheduler hook
-	# instead of an IO object. Verify we handle both forms without raising.
-	it "can close a raw Integer fd" do
-		selector = subject.new(Fiber.current)
-		next unless selector.respond_to?(:io_close)
-		
-		input, output = IO.pipe
-		
-		# Hand ownership of the fd to io_close so Ruby won't double-close it.
+		# Hand ownership of the fd to `io_close` so Ruby won't double-close it.
 		input.autoclose = false
-		fd = input.fileno
+		descriptor = input.fileno
 		
 		begin
-			expect(selector.io_close(fd)).to be_truthy
+			expect(selector.io_close(descriptor)).to be_truthy
 		ensure
 			input.close rescue nil
 			output.close rescue nil
@@ -47,8 +31,20 @@
 IO::Event::Selector.constants.each do |name|
 	klass = IO::Event::Selector.const_get(name)
 	next unless klass.respond_to?(:new)
+	next unless klass.method_defined?(:io_close)
 	
 	describe(klass, unique: name) do
 		it_behaves_like IOClose
 	end
+	
+	# `Debug::Selector` should transparently forward `io_close` to any wrapped selector that implements it (see `Forwarders`). The shared examples build the selector via `subject.new(loop)`, so we hand them a thin factory that closes over the underlying selector class.
+	debug_class = Class.new do
+		define_singleton_method(:new) do |loop|
+			IO::Event::Debug::Selector.new(klass.new(loop))
+		end
+	end
+	
+	describe(debug_class, unique: "Debug(#{name})") do
+		it_behaves_like IOClose
+	end
 end