diff --git a/jrx/src/b_lib.ts b/jrx/src/b_lib.ts
index 3ff8c65..2a86090 100644
--- a/jrx/src/b_lib.ts
+++ b/jrx/src/b_lib.ts
@@ -384,9 +384,16 @@ tx_sign
     : Promise<{signedTransaction : string}>
 {
     let tx_bytes        : Uint8Array = (await vdk_aeser.unbaseNcheck(tx_str)).bytes;
+    // thank you ulf
+    // https://github.com/aeternity/protocol/tree/fd179822fc70241e79cbef7636625cf344a08109/consensus#transaction-signature
+    // we sign <<NetworkId, SerializedObject>>
+    // SerializedObject can either be the object or the hash of the object
+    // let's stick with hash for now
+    let network_id      : Uint8Array = vdk_binary.encode_utf8('ae_uat');
     let tx_hash_bytes   : Uint8Array = hash(tx_bytes);
+    let sign_data       : Uint8Array = vdk_binary.bytes_concat(network_id, tx_hash_bytes);
     // @ts-ignore yes nacl is stupid
-    let signature       : Uint8Array = nacl.sign.detached(tx_hash_bytes, secret_key);
+    let signature       : Uint8Array = nacl.sign.detached(sign_data, secret_key);
     let signed_tx_bytes : Uint8Array = vdk_aeser.signed_tx([signature], tx_bytes);
     let signed_tx_str   : string     = await vdk_aeser.baseNcheck('tx', signed_tx_bytes);
     return {signedTransaction: signed_tx_str};