diff --git a/lib/postgresql_interface.js b/lib/postgresql_interface.js
index bcae7cbd..0d514e60 100644
--- a/lib/postgresql_interface.js
+++ b/lib/postgresql_interface.js
@@ -3,6 +3,7 @@
 
 // TODO: Consider using serializable transactions for true ACID
 
+var BigNumber = require('bignumber.js')
 var pg = require('pg');
 var async = require('async');
 var _ = require('lodash');
@@ -173,27 +174,30 @@ function billsAndTxs(client, session, cb) {
     // we need to parse, since we know these won't be huge numbers.
     cb(null, {
       billsFiat: parseInt(results[0].rows[0].fiat),
-      billsSatoshis: parseInt(results[0].rows[0].satoshis),
+      billsSatoshis: new BigNumber(results[0].rows[0].satoshis),
       txFiat: parseInt(results[1].rows[0].fiat),
-      txSatoshis: parseInt(results[1].rows[0].satoshis)
+      txSatoshis: new BigNumber(results[1].rows[0].satoshis)
     });
   });
 }
 
 function computeSendAmount(tx, totals) {
   var fiatRemaining = (tx.fiat || totals.billsFiat) - totals.txFiat;
-  var satoshisRemaining = (tx.satoshis || totals.billsSatoshis) -
-    totals.txSatoshis;
+
+  var satoshisRemaining = tx.satoshis.eq(0)
+  ? totals.billsSatoshis.minus(totals.txSatoshis)
+  : tx.satoshis.minus(totals.txSatoshis)
+
   var result = {
     fiat: fiatRemaining,
     satoshis: satoshisRemaining
   };
-  if (result.fiat < 0 || result.satoshis < 0) {
+  if (result.fiat < 0 || result.satoshis.lt(0)) {
     logger.warn({tx: tx, totals: totals, result: result},
       'computeSendAmount result < 0, this shouldn\'t happen. ' +
       'Maybe timeout arrived after machineSend.');
     result.fiat = 0;
-    result.satoshis = 0;
+    result.satoshis = new BigNumber(0);
   }
   return result;
 }
@@ -240,7 +244,7 @@ function insertOutgoingTx(client, session, tx, totals, cb) {
   var authority = tx.fiat ? 'machine' : 'timeout';
   var satoshis = sendAmount.satoshis;
   var fiat = sendAmount.fiat;
-  if (satoshis === 0) return cb(null, {satoshis: 0, fiat: 0});
+  if (satoshis.eq(0)) return cb(null, {satoshis: new BigNumber(0), fiat: 0});
 
   insertOutgoing(client, session, tx, satoshis, fiat, stage, authority,
       function(err) {
@@ -264,7 +268,7 @@ function insertOutgoingCompleteTx(client, session, tx, cb) {
 
 function insertIncoming(client, session, tx, satoshis, fiat, stage, authority,
     cb) {
-  var realSatoshis = satoshis || 0;
+  var realSatoshis = satoshis || new BigNumber(0);
   insertTx(client, session, true, tx, realSatoshis, fiat, stage, authority, cb);
 }