diff --git a/lib/io/event/selector/select.rb b/lib/io/event/selector/select.rb
index d99e8a3..e5e7f67 100644
--- a/lib/io/event/selector/select.rb
+++ b/lib/io/event/selector/select.rb
@@ -168,6 +168,8 @@ def again?(errno)
 			if Support.fiber_scheduler_v3?
 				# Ruby 3.3+, full IO::Buffer support.
 				
+				# Read from the given IO to the buffer.
+				#
 				# @parameter length [Integer] The minimum number of bytes to read.
 				# @parameter offset [Integer] The offset into the buffer to read to.
 				def io_read(fiber, io, buffer, length, offset = 0)
@@ -196,6 +198,8 @@ def io_read(fiber, io, buffer, length, offset = 0)
 					return total
 				end
 				
+				# Write to the given IO from the buffer.
+				#
 				# @parameter length [Integer] The minimum number of bytes to write.
 				# @parameter offset [Integer] The offset into the buffer to write from.
 				def io_write(fiber, io, buffer, length, offset = 0)
diff --git a/lib/io/event/support.rb b/lib/io/event/support.rb
index b9a937e..42305ac 100644
--- a/lib/io/event/support.rb
+++ b/lib/io/event/support.rb
@@ -10,14 +10,23 @@ def self.buffer?
 				IO.const_defined?(:Buffer)
 			end
 			
+			# To be removed on 31 Mar 2025.
 			def self.fiber_scheduler_v1?
 				IO.const_defined?(:Buffer) and !Fiber.respond_to?(:blocking)
 			end
 			
+			# To be removed on 31 Mar 2026.
 			def self.fiber_scheduler_v2?
+				# Some interface changes were back-ported incorrectly:
+				# https://github.com/ruby/ruby/pull/10778
+				# Specifically "Improvements to IO::Buffer read/write/pread/pwrite."
+				# Missing correct size calculation.
+				return false if RUBY_VERSION >= "3.2.5"
+				
 				IO.const_defined?(:Buffer) and Fiber.respond_to?(:blocking) and IO::Buffer.instance_method(:read).arity == -1
 			end
 			
+			# To become the default 31 Mar 2026.
 			def self.fiber_scheduler_v3?
 				if fiber_scheduler_v2?
 					return true if RUBY_VERSION >= "3.3"
diff --git a/test/io/event/selector/buffered_io.rb b/test/io/event/selector/buffered_io.rb
index 4985733..9c4e209 100644
--- a/test/io/event/selector/buffered_io.rb
+++ b/test/io/event/selector/buffered_io.rb
@@ -41,11 +41,13 @@
 		it "can read and write at the specified offset" do
 			writer = Fiber.new do
 				buffer = IO::Buffer.new(128)
+				# We can't write 128 bytes because there are only +64 bytes from offset 64.
 				expect(selector.io_write(Fiber.current, output, buffer, 128, 64)).to be == 64
 			end
 			
 			reader = Fiber.new do
 				buffer = IO::Buffer.new(128)
+				# Only 64 bytes are available to read.
 				expect(selector.io_read(Fiber.current, input, buffer, 1, 64)).to be == 64
 			end