diff --git a/index.js b/index.js
index bbbf2cf..f96dd56 100644
--- a/index.js
+++ b/index.js
@@ -88,7 +88,7 @@ class I2CPort {
             /** Different from Web I2C API specification. */
             writeBytes: async (bytes) => {
                 try {
-                    const { bytesWritten, buffer } = await bus.i2cWrite(slaveAddress, length, Buffer.from(bytes));
+                    const { bytesWritten, buffer } = await bus.i2cWrite(slaveAddress, bytes.length, Buffer.from(bytes));
                     return new Uint8Array(buffer.slice(0, bytesWritten));
                 }
                 catch (error) {
diff --git a/index.ts b/index.ts
index e9dd73f..7af2cf4 100644
--- a/index.ts
+++ b/index.ts
@@ -110,7 +110,7 @@ export class I2CPort {
         try {
           const { bytesWritten, buffer } = await bus.i2cWrite(
             slaveAddress,
-            length,
+            bytes.length,
             Buffer.from(bytes)
           );
           return new Uint8Array(buffer.slice(0, bytesWritten));