diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index 6810b591..3b39e386 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -28,12 +28,6 @@ jobs:
         experimental: [false]
         
         include:
-          - os: ubuntu
-            ruby: truffleruby
-            experimental: true
-          - os: ubuntu
-            ruby: jruby
-            experimental: true
           - os: ubuntu
             ruby: head
             experimental: true
diff --git a/async.gemspec b/async.gemspec
index fc1e6918..a2cdd79f 100644
--- a/async.gemspec
+++ b/async.gemspec
@@ -24,6 +24,7 @@ Gem::Specification.new do |spec|
 	spec.files = Dir.glob(["{lib}/**/*", "*.md"], File::FNM_DOTMATCH, base: __dir__)
 	
 	spec.required_ruby_version = ">= 3.2"
+	spec.required_ruby_engine = "ruby"
 	
 	spec.add_dependency "console", "~> 1.29"
 	spec.add_dependency "fiber-annotation"
diff --git a/lib/async/scheduler.rb b/lib/async/scheduler.rb
index 568a5ff2..e015e0eb 100644
--- a/lib/async/scheduler.rb
+++ b/lib/async/scheduler.rb
@@ -347,7 +347,7 @@ def io_read(io, buffer, length, offset = 0)
 				timer&.cancel!
 			end
 			
-			if RUBY_ENGINE != "ruby" || RUBY_VERSION >= "3.3.1"
+			if RUBY_VERSION >= "3.3.1"
 				# Write the specified buffer to the IO.
 				#
 				# @public Since *Async v2* and *Ruby v3.3.1* with `IO::Buffer` support.