diff --git a/rust/src/tx_builder.rs b/rust/src/tx_builder.rs
index 61053060..fd40cd2e 100644
--- a/rust/src/tx_builder.rs
+++ b/rust/src/tx_builder.rs
@@ -37,17 +37,20 @@ fn witness_keys_for_cert(cert_enum: &Certificate, keys: &mut BTreeSet<Ed25519Key
     }
 }
 
+fn fake_private_key() -> Bip32PrivateKey {
+    Bip32PrivateKey::from_bytes(
+        &[0xb8, 0xf2, 0xbe, 0xce, 0x9b, 0xdf, 0xe2, 0xb0, 0x28, 0x2f, 0x5b, 0xad, 0x70, 0x55, 0x62, 0xac, 0x99, 0x6e, 0xfb, 0x6a, 0xf9, 0x6b, 0x64, 0x8f,
+            0x44, 0x45, 0xec, 0x44, 0xf4, 0x7a, 0xd9, 0x5c, 0x10, 0xe3, 0xd7, 0x2f, 0x26, 0xed, 0x07, 0x54, 0x22, 0xa3, 0x6e, 0xd8, 0x58, 0x5c, 0x74, 0x5a,
+            0x0e, 0x11, 0x50, 0xbc, 0xce, 0xba, 0x23, 0x57, 0xd0, 0x58, 0x63, 0x69, 0x91, 0xf3, 0x8a, 0x37, 0x91, 0xe2, 0x48, 0xde, 0x50, 0x9c, 0x07, 0x0d,
+            0x81, 0x2a, 0xb2, 0xfd, 0xa5, 0x78, 0x60, 0xac, 0x87, 0x6b, 0xc4, 0x89, 0x19, 0x2c, 0x1e, 0xf4, 0xce, 0x25, 0x3c, 0x19, 0x7e, 0xe2, 0x19, 0xa4]
+    ).unwrap()
+}
+
 // tx_body must be the result of building from tx_builder
 // constructs the rest of the Transaction using fake witness data of the correct length
 // for use in calculating the size of the final Transaction
 fn fake_full_tx(tx_builder: &TransactionBuilder, body: TransactionBody) -> Result<Transaction, JsError> {
-    // bytes for Bip32: art forum devote street sure rather head chuckle guard poverty release quote oak craft enemy
-    let fake_key_root = Bip32PrivateKey::from_bytes(
-        &[0xb8, 0xf2, 0xbe, 0xce, 0x9b, 0xdf, 0xe2, 0xb0, 0x28, 0x2f, 0x5b, 0xad, 0x70, 0x55, 0x62, 0xac, 0x99, 0x6e, 0xfb, 0x6a, 0xf9, 0x6b, 0x64, 0x8f,
-          0x44, 0x45, 0xec, 0x44, 0xf4, 0x7a, 0xd9, 0x5c, 0x10, 0xe3, 0xd7, 0x2f, 0x26, 0xed, 0x07, 0x54, 0x22, 0xa3, 0x6e, 0xd8, 0x58, 0x5c, 0x74, 0x5a,
-          0x0e, 0x11, 0x50, 0xbc, 0xce, 0xba, 0x23, 0x57, 0xd0, 0x58, 0x63, 0x69, 0x91, 0xf3, 0x8a, 0x37, 0x91, 0xe2, 0x48, 0xde, 0x50, 0x9c, 0x07, 0x0d,
-          0x81, 0x2a, 0xb2, 0xfd, 0xa5, 0x78, 0x60, 0xac, 0x87, 0x6b, 0xc4, 0x89, 0x19, 0x2c, 0x1e, 0xf4, 0xce, 0x25, 0x3c, 0x19, 0x7e, 0xe2, 0x19, 0xa4]
-    ).unwrap();
+    let fake_key_root = fake_private_key();
 
     // recall: this includes keys for input, certs and withdrawals
     let vkeys = match tx_builder.input_types.vkeys.len() {
@@ -606,6 +609,19 @@ mod tests {
         index | 0x80_00_00_00
     }
 
+    #[test]
+    fn check_fake_private_key() {
+        let fpk = fake_private_key();
+        assert_eq!(
+            fpk.to_bech32(),
+            "xprv1hretan5mml3tq2p0twkhq4tz4jvka7m2l94kfr6yghkyfar6m9wppc7h9unw6p65y23kakzct3695rs32z7vaw3r2lg9scmfj8ec5du3ufydu5yuquxcz24jlkjhsc9vsa4ufzge9s00fn398svhacse5su2awrw",
+        );
+        assert_eq!(
+            fpk.to_public().to_bech32(),
+            "xpub1eamrnx3pph58yr5l4z2wghjpu2dt2f0rp0zq9qquqa39p52ct0xercjgmegfcpcdsy4t9ld90ps2epmtcjy3jtq77n8z20qe0m3pnfqntgrgj",
+        );
+    }
+
     #[test]
     fn build_tx_with_change() {
         let linear_fee = LinearFee::new(&to_bignum(500), &to_bignum(2));