diff --git a/electrum/invoices.py b/electrum/invoices.py
index a22557a0a..e8a9ca4f9 100644
--- a/electrum/invoices.py
+++ b/electrum/invoices.py
@@ -223,7 +223,7 @@ class LNInvoice(Invoice):
         d = self.to_json()
         d.update({
             'pubkey': self._lnaddr.pubkey.serialize().hex(),
-            'amount_BTC': self._lnaddr.amount,
+            'amount_BTC': str(self._lnaddr.amount),
             'rhash': self._lnaddr.paymenthash.hex(),
             'description': self._lnaddr.get_description(),
             'exp': self._lnaddr.get_expiry(),