diff --git a/src/constants.rs b/src/constants.rs
index 844aa1c..cf8acbe 100644
--- a/src/constants.rs
+++ b/src/constants.rs
@@ -4,6 +4,8 @@ pub const PACKET_SIZE: usize = 512;
 #[cfg(not(feature = "highspeed-usb"))]
 pub const PACKET_SIZE: usize = 64;
 
+pub const CCID_HEADER_LEN: usize = 10;
+
 pub const CLASS_CCID: u8 = 0x0B;
 pub const SUBCLASS_NONE: u8 = 0x0;
 
@@ -39,7 +41,7 @@ pub const MAX_IFSD: [u8; 4] = [0xfe, 0x00, 0x00, 0x00];
 // "The value shall be between 261 + 10 and 65544 + 10
 // dwMaxCCIDMsgLen 3072
 pub const MAX_MSG_LENGTH: usize = 3072;
-pub const MAX_MSG_LENGTH_LE: [u8; 4] = [0x00, 0x0C, 0x00, 0x00];
+pub const MAX_MSG_LENGTH_LE: [u8; 4] = (MAX_MSG_LENGTH as u32).to_le_bytes();
 
 pub const NUM_SLOTS: u8 = 1;
 pub const MAX_BUSY_SLOTS: u8 = 1;
diff --git a/src/pipe.rs b/src/pipe.rs
index 4ffe6c7..9a5df4c 100644
--- a/src/pipe.rs
+++ b/src/pipe.rs
@@ -145,7 +145,7 @@ where
         // when certificates are transmitted, because PIV somehow uses short APDUs
         // only (can we fix this), so 255B is the maximum)
         if !self.receiving_long {
-            if packet.len() < 10 {
+            if packet.len() < CCID_HEADER_LEN {
                 panic!("unexpected short packet");
             }
             self.ext_packet.clear();
@@ -304,7 +304,7 @@ where
         if self.state == State::Processing {
             // Need to send a wait extension request.
             let mut packet = RawPacket::new();
-            packet.resize_default(10).ok();
+            packet.resize_default(CCID_HEADER_LEN).ok();
             packet[0] = 0x80;
             packet[6] = self.seq;
 
@@ -369,7 +369,7 @@ where
             panic!("No response while priming outbox");
         };
 
-        let chunk_size = core::cmp::min(PACKET_SIZE - 10, message.len() - self.sent);
+        let chunk_size = core::cmp::min(PACKET_SIZE - CCID_HEADER_LEN, message.len() - self.sent);
         let chunk = &message[self.sent..][..chunk_size];
         self.sent += chunk_size;
         let more = self.sent < message.len();
@@ -409,7 +409,7 @@ where
 
     fn send_slot_status_ok(&mut self) {
         let mut packet = RawPacket::new();
-        packet.resize_default(10).ok();
+        packet.resize_default(CCID_HEADER_LEN).ok();
         packet[0] = 0x81;
         packet[6] = self.seq;
         self.send_packet_assuming_possible(packet);
@@ -417,7 +417,7 @@ where
 
     fn send_slot_status_error(&mut self, error: Error) {
         let mut packet = RawPacket::new();
-        packet.resize_default(10).ok();
+        packet.resize_default(CCID_HEADER_LEN).ok();
         packet[0] = 0x6c;
         packet[6] = self.seq;
         packet[7] = 1 << 6;
diff --git a/src/types/packet.rs b/src/types/packet.rs
index 09ceb1a..d1e7ec3 100644
--- a/src/types/packet.rs
+++ b/src/types/packet.rs
@@ -45,9 +45,9 @@ pub trait PacketWithData: Packet {
     fn data(&self) -> &[u8] {
         // let len = u32::from_le_bytes(self[1..5].try_into().unwrap()) as usize;
         let declared_len = u32::from_le_bytes(self[1..5].try_into().unwrap()) as usize;
-        let len = core::cmp::min(MAX_MSG_LENGTH - 10, declared_len);
+        let len = core::cmp::min(MAX_MSG_LENGTH - CCID_HEADER_LEN, declared_len);
         // hprintln!("delcared = {}, len = {}", declared_len, len).ok();
-        &self[10..][..len]
+        &self[CCID_HEADER_LEN..][..len]
     }
 }
 
@@ -76,7 +76,7 @@ pub struct DataBlock<'a> {
 
 impl<'a> DataBlock<'a> {
     pub fn new(seq: u8, chain: Chain, data: &'a [u8]) -> Self {
-        assert!(data.len() + 10 <= PACKET_SIZE);
+        assert!(data.len() + CCID_HEADER_LEN <= PACKET_SIZE);
         Self { seq, chain, data }
     }
 }
@@ -117,7 +117,7 @@ impl From<DataBlock<'_>> for RawPacket {
     fn from(block: DataBlock<'_>) -> RawPacket {
         let mut packet = RawPacket::new();
         let len = block.data.len();
-        packet.resize_default(10 + len).ok();
+        packet.resize_default(CCID_HEADER_LEN + len).ok();
         packet[0] = 0x80;
         packet[1..][..4].copy_from_slice(
             &u32::try_from(len)
@@ -133,7 +133,7 @@ impl From<DataBlock<'_>> for RawPacket {
         packet[8] = 0;
         // chain parameter
         packet[9] = block.chain as u8;
-        packet[10..][..len].copy_from_slice(block.data);
+        packet[CCID_HEADER_LEN..][..len].copy_from_slice(block.data);
 
         packet
     }
@@ -224,7 +224,7 @@ macro_rules! command_message {
             fn try_from(packet: ExtPacket)
                 -> core::result::Result<Self, Self::Error>
             {
-                if packet.len() < 10 {
+                if packet.len() <CCID_HEADER_LEN {
                     return Err(Error::ShortPacket);
                 }
                 if packet[5] != 0 {