diff --git a/src/ctap/hid/mod.rs b/src/ctap/hid/mod.rs
index 7489f6e..3a96699 100644
--- a/src/ctap/hid/mod.rs
+++ b/src/ctap/hid/mod.rs
@@ -227,44 +227,35 @@ impl CtapHid {
                     }
                     // CTAP specification (version 20190130) section 8.1.9.1.3
                     CtapHid::COMMAND_INIT => {
-                        if cid == CtapHid::CHANNEL_BROADCAST {
-                            if message.payload.len() != 8 {
-                                return CtapHid::error_message(cid, CtapHid::ERR_INVALID_LEN);
-                            }
+                        if message.payload.len() != 8 {
+                            return CtapHid::error_message(cid, CtapHid::ERR_INVALID_LEN);
+                        }
 
+                        let new_cid = if cid == CtapHid::CHANNEL_BROADCAST {
                             // TODO: Prevent allocating 2^32 channels.
                             self.allocated_cids += 1;
-                            let allocated_cid = (self.allocated_cids as u32).to_ne_bytes();
-
-                            let mut payload = vec![0; 17];
-                            payload[..8].copy_from_slice(&message.payload);
-                            payload[8..12].copy_from_slice(&allocated_cid);
-                            payload[12] = CtapHid::PROTOCOL_VERSION;
-                            payload[13] = CtapHid::DEVICE_VERSION_MAJOR;
-                            payload[14] = CtapHid::DEVICE_VERSION_MINOR;
-                            payload[15] = CtapHid::DEVICE_VERSION_BUILD;
-                            payload[16] = CtapHid::CAPABILITIES;
-
-                            // This unwrap is safe because the payload length is 17 <= 7609 bytes.
-                            CtapHid::split_message(Message {
-                                cid,
-                                cmd: CtapHid::COMMAND_INIT,
-                                payload,
-                            })
-                            .unwrap()
+                            (self.allocated_cids as u32).to_ne_bytes()
                         } else {
                             // Sync the channel and discard the current transaction.
-                            // TODO: The specification (version 20190130) wording isn't clear about
-                            // the payload format in this case.
-                            //
-                            // This unwrap is safe because the payload length is 0 <= 7609 bytes.
-                            CtapHid::split_message(Message {
-                                cid,
-                                cmd: CtapHid::COMMAND_INIT,
-                                payload: vec![],
-                            })
-                            .unwrap()
-                        }
+                            cid
+                        };
+
+                        let mut payload = vec![0; 17];
+                        payload[..8].copy_from_slice(&message.payload);
+                        payload[8..12].copy_from_slice(&new_cid);
+                        payload[12] = CtapHid::PROTOCOL_VERSION;
+                        payload[13] = CtapHid::DEVICE_VERSION_MAJOR;
+                        payload[14] = CtapHid::DEVICE_VERSION_MINOR;
+                        payload[15] = CtapHid::DEVICE_VERSION_BUILD;
+                        payload[16] = CtapHid::CAPABILITIES;
+
+                        // This unwrap is safe because the payload length is 17 <= 7609 bytes.
+                        CtapHid::split_message(Message {
+                            cid,
+                            cmd: CtapHid::COMMAND_INIT,
+                            payload,
+                        })
+                        .unwrap()
                     }
                     // CTAP specification (version 20190130) section 8.1.9.1.4
                     CtapHid::COMMAND_PING => {
@@ -568,6 +559,66 @@ mod test {
         );
     }
 
+    #[test]
+    fn test_command_init_for_sync() {
+        let mut rng = ThreadRng256 {};
+        let user_immediately_present = |_| Ok(());
+        let mut ctap_state = CtapState::new(&mut rng, user_immediately_present);
+        let mut ctap_hid = CtapHid::new();
+        let cid = cid_from_init(&mut ctap_hid, &mut ctap_state);
+
+        // Ping packet with a length longer than one packet.
+        let mut packet1 = [0x51; 64];
+        packet1[..4].copy_from_slice(&cid);
+        packet1[4..7].copy_from_slice(&[0x81, 0x02, 0x00]);
+        // Init packet on the same channel.
+        let mut packet2 = [0x00; 64];
+        packet2[..4].copy_from_slice(&cid);
+        packet2[4..15].copy_from_slice(&[
+            0x86, 0x00, 0x08, 0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE, 0xF0,
+        ]);
+        let mut result = Vec::new();
+        let mut assembler_reply = MessageAssembler::new();
+        for pkt_request in &[packet1, packet2] {
+            for pkt_reply in
+                ctap_hid.process_hid_packet(&pkt_request, DUMMY_CLOCK_VALUE, &mut ctap_state)
+            {
+                if let Some(message) = assembler_reply
+                    .parse_packet(&pkt_reply, DUMMY_TIMESTAMP)
+                    .unwrap()
+                {
+                    result.push(message);
+                }
+            }
+        }
+        assert_eq!(
+            result,
+            vec![Message {
+                cid,
+                cmd: CtapHid::COMMAND_INIT,
+                payload: vec![
+                    0x12, // Nonce
+                    0x34,
+                    0x56,
+                    0x78,
+                    0x9A,
+                    0xBC,
+                    0xDE,
+                    0xF0,
+                    cid[0], // Allocated CID
+                    cid[1],
+                    cid[2],
+                    cid[3],
+                    0x02, // Protocol version
+                    0x00, // Device version
+                    0x00,
+                    0x00,
+                    CtapHid::CAPABILITIES
+                ]
+            }]
+        );
+    }
+
     #[test]
     fn test_command_ping() {
         let mut rng = ThreadRng256 {};
diff --git a/src/ctap/hid/receive.rs b/src/ctap/hid/receive.rs
index fef51a4..b522837 100644
--- a/src/ctap/hid/receive.rs
+++ b/src/ctap/hid/receive.rs
@@ -586,5 +586,33 @@ mod test {
         );
     }
 
+    #[test]
+    fn test_init_sync() {
+        let mut assembler = MessageAssembler::new();
+        // Ping packet with a length longer than one packet.
+        assert_eq!(
+            assembler.parse_packet(
+                &byte_extend(&[0x12, 0x34, 0x56, 0x78, 0x81, 0x02, 0x00], 0x51),
+                DUMMY_TIMESTAMP
+            ),
+            Ok(None)
+        );
+        // Init packet on the same channel.
+        assert_eq!(
+            assembler.parse_packet(
+                &zero_extend(&[
+                    0x12, 0x34, 0x56, 0x78, 0x86, 0x00, 0x08, 0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC,
+                    0xDE, 0xF0
+                ]),
+                DUMMY_TIMESTAMP
+            ),
+            Ok(Some(Message {
+                cid: [0x12, 0x34, 0x56, 0x78],
+                cmd: 0x06,
+                payload: vec![0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE, 0xF0]
+            }))
+        );
+    }
+
     // TODO: more tests
 }