May be native IO. Don't try to clear reactor.

lib/async/io/shared_endpoint.rb

@@ -24,7 +24,10 @@ def self.bound(endpoint, backlog: Socket::SOMAXCONN, close_on_exec: false, **opt
 					end
 
 					server.close_on_exec = close_on_exec
-					server.reactor = nil
+
+					if server.respond_to?(:reactor=)
+						server.reactor = nil
+					end
 				end
 
 				return self.new(endpoint, wrappers)
@@ -35,7 +38,10 @@ def self.connected(endpoint, close_on_exec: false)
 				wrapper = endpoint.connect
 
 				wrapper.close_on_exec = close_on_exec
-				wrapper.reactor = nil
+
+				if wrapper.respond_to?(:reactor=)
+					wrapper.reactor = nil
+				end
 
 				return self.new(endpoint, [wrapper])
 			end