diff --git a/src/messages/userDataRequest.ts b/src/messages/userDataRequest.ts
index 4465d08..b7d25d4 100644
--- a/src/messages/userDataRequest.ts
+++ b/src/messages/userDataRequest.ts
@@ -33,9 +33,11 @@ export function packUserDataRequestMessage (properties: UserDataRequestMessage,
   const packedData = new SmartBuffer()
   packedData.writeBytes(usernameLength)
   packedData.writeBytes(username)
+  packedData.pad(32 - username.length)
   packedData.writeBytes(colour)
   packedData.writeBytes(clientIdLength)
   packedData.writeBytes(clientId)
+  packedData.pad(32 - clientId.length)
 
   // Encrypt the data.
   const data = encrypt(packedData.data, MESSAGE_TYPE, key)
diff --git a/src/messages/userDataResponse.ts b/src/messages/userDataResponse.ts
index fe8ceba..efea90f 100644
--- a/src/messages/userDataResponse.ts
+++ b/src/messages/userDataResponse.ts
@@ -33,9 +33,11 @@ export function packUserDataResponseMessage (properties: UserDataResponseMessage
   const packedData = new SmartBuffer()
   packedData.writeBytes(usernameLength)
   packedData.writeBytes(username)
+  packedData.pad(32 - username.length)
   packedData.writeBytes(colour)
   packedData.writeBytes(clientIdLength)
   packedData.writeBytes(clientId)
+  packedData.pad(32 - clientId.length)
 
   // Return encrypted data.
   const data = encrypt(packedData.data, MESSAGE_TYPE, key)
diff --git a/src/utilities/smart-buffer.ts b/src/utilities/smart-buffer.ts
index c7dbea1..3c80031 100644
--- a/src/utilities/smart-buffer.ts
+++ b/src/utilities/smart-buffer.ts
@@ -79,7 +79,8 @@ export class SmartBuffer {
   * @param length The number of bytes to pad.
   */
   pad (length: number): void {
-    this._data.push(...Array<number>(length))
+    this._data.push(...Array<number>(length).fill(0))
+    this.cursor += length
   }
 
   /**
@@ -100,7 +101,7 @@ export class SmartBuffer {
    */
   splice (start: number, deleteCount: number, ...items: number[]): void {
     if (this.length < start) {
-      this.pad(start)
+      this._data.push(...Array<number>(start))
     }
     this._data.splice(this.cursor, deleteCount, ...items)
   }
diff --git a/tests/messages/userDataRequest.test.ts b/tests/messages/userDataRequest.test.ts
index e7e2973..7b6b822 100644
--- a/tests/messages/userDataRequest.test.ts
+++ b/tests/messages/userDataRequest.test.ts
@@ -23,10 +23,10 @@ test('Create a user data request (0x0002) packet.', () => {
   // Then
   // We can't check the contents of the data as it's encrypted with a random nonce.
   // Check the message type and length.
-  expect(packedPacket.slice(0, 4)).toMatchObject(new Uint8Array([0x00, 0x02, 0x00, 0x3A]))
+  expect(packedPacket.slice(0, 4)).toMatchObject(new Uint8Array([0x00, 0x02, 0x00, 0x67]))
 
   // Check the total length is as expected.
-  expect(packedPacket.length).toBe(62)
+  expect(packedPacket.length).toBe(107)
 })
 
 test('Parse a user data request (0x0002).', () => {
diff --git a/tests/messages/userDataResponse.test.ts b/tests/messages/userDataResponse.test.ts
index 99ca6f0..c957dd3 100644
--- a/tests/messages/userDataResponse.test.ts
+++ b/tests/messages/userDataResponse.test.ts
@@ -23,10 +23,10 @@ test('Create a user data response (0x0003) packet.', () => {
   // Then
   // We can't check the contents of the data as it's encrypted with a random nonce.
   // Check the message type and length.
-  expect(packedPacket.slice(0, 4)).toMatchObject(new Uint8Array([0x00, 0x03, 0x00, 0x3A]))
+  expect(packedPacket.slice(0, 4)).toMatchObject(new Uint8Array([0x00, 0x03, 0x00, 0x67]))
 
   // Check the total length is as expected.
-  expect(packedPacket.length).toBe(62)
+  expect(packedPacket.length).toBe(107)
 })
 
 test('Parse a user data response (0x0003).', () => {