diff --git a/nip04.js b/nip04.js
index 1e715b0..e89dcee 100644
--- a/nip04.js
+++ b/nip04.js
@@ -36,5 +36,5 @@ export function decrypt(privkey, pubkey, ciphertext) {
 }
 
 function getOnlyXFromFullSharedSecret(fullSharedSecretCoordinates) {
-  return fullSharedSecretCoordinates.substr(2, 64)
+  return Buffer.from(fullSharedSecretCoordinates).toString('hex').substr(2, 64)
 }
diff --git a/package.json b/package.json
index ad93629..336d4b5 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "nostr-tools",
-  "version": "0.21.0",
+  "version": "0.21.1",
   "description": "Tools for making a Nostr client.",
   "repository": {
     "type": "git",