diff --git a/Sources/SwiftRPLidar/LidarSerial.swift b/Sources/SwiftRPLidar/LidarSerial.swift
index 1aa44b3..3fc9d57 100644
--- a/Sources/SwiftRPLidar/LidarSerial.swift
+++ b/Sources/SwiftRPLidar/LidarSerial.swift
@@ -3,8 +3,8 @@ import Foundation
 public protocol LidarSerial {
     var dtr: Bool {get set};
     var inWaiting: Int {get};
-    func closePort() -> Void;
-    func openPort() -> Void;
+    func closePort();
+    func openPort() throws;
     func readData(ofLength: Int) throws -> Data;
-    func writeData(_ data: Data) throws -> Void;
+    func writeData(_ data: Data) throws -> Int;
 }