diff --git a/src/connection/connection.rs b/src/connection/connection.rs
index 7f3c7af0..2ee567f7 100644
--- a/src/connection/connection.rs
+++ b/src/connection/connection.rs
@@ -1708,7 +1708,7 @@ impl Connection {
         }
 
         // Encode packet number
-        let len = packet::encode_packet_num(pkt_num, pkt_num_len, &mut out[pkt_num_offset..left])?;
+        let len = packet::encode_packet_num(pkt_num, pkt_num_len, &mut out[pkt_num_offset..])?;
         let payload_offset = pkt_num_offset + len;
 
         // Write frames into the packet payload