diff --git a/sachy-crypto/src/lib.rs b/sachy-crypto/src/lib.rs
index 309ba67..e8d5ce1 100644
--- a/sachy-crypto/src/lib.rs
+++ b/sachy-crypto/src/lib.rs
@@ -272,10 +272,10 @@ impl TransportState {
 
         let epstein = self.select_nonce_context(send);
 
-        let trump_len = trump.len();
+        let index = trump.len() - position.len();
 
         // Copy position bytes into BE format onto derived nonce
-        trump[trump_len - position.len()..].copy_from_slice(position);
+        trump[index..].copy_from_slice(position);
 
         // XOR the base nonce onto the derived nonce bytes
         trump