diff --git a/dev/double-spend-scenario.js b/dev/double-spend-scenario.js
new file mode 100644
index 00000000..eef96ccb
--- /dev/null
+++ b/dev/double-spend-scenario.js
@@ -0,0 +1,60 @@
+var db = require('../lib/postgresql_interface')
+var connectionString = 'postgres://lamassu:lamassu@localhost/lamassu'
+db.init(connectionString)
+
+var session = {
+  id: '6ede611c-cd03-11e5-88ee-2b5fcfdb0bc2',
+  fingerprint: 'xx:xx'
+}
+var tx = {
+  fiat: 40,
+  satoshis: 6980000,
+  toAddress: '1xxx',
+  currencyCode: 'CAD',
+  incoming: false
+}
+
+var tx2 = {
+  fiat: 0,
+  satoshis: 6980000,
+  toAddress: '1xxx',
+  currencyCode: 'CAD',
+  incoming: false
+}
+
+db.addOutgoingTx(session, tx, function (err, res) {
+  console.log('DEBUG1')
+  console.log(err)
+  console.log(res)
+})
+
+db.addOutgoingTx(session, tx2, function (err, res) {
+  console.log('DEBUG2')
+  console.log(err)
+  console.log(res)
+})
+
+/*
+setTimeout(function () {
+  db.addOutgoingTx(session, tx2, function (err, res) {
+    console.log('DEBUG2')
+    console.log(err)
+    console.log(res)
+  })
+}, 0)
+*/
+
+var bills = {
+  uuid: 'c630338c-cd03-11e5-a9df-dbc9be2e9fbb',
+  currency: 'CAD',
+  toAddress: '1xxx',
+  deviceTime: Date.now(),
+  satoshis: 6980000,
+  fiat: 40
+}
+
+/*
+db.recordBill(session, bills, function (err) {
+  console.log(err)
+})
+*/
diff --git a/lib/postgresql_interface.js b/lib/postgresql_interface.js
index e969f3d8..ca58093d 100644
--- a/lib/postgresql_interface.js
+++ b/lib/postgresql_interface.js
@@ -347,6 +347,7 @@ exports.addOutgoingTx = function addOutgoingTx(session, tx, cb) {
     if (cerr) return cb(cerr);
     async.series([
       async.apply(silentQuery, client, 'BEGIN'),
+      async.apply(silentQuery, client, 'LOCK TABLE transactions'),
       async.apply(insertOutgoingCompleteTx, client, session, tx),
       async.apply(removePendingTx, client, session),
       async.apply(buildOutgoingTx, client, session, tx)
@@ -357,7 +358,7 @@ exports.addOutgoingTx = function addOutgoingTx(session, tx, cb) {
       }
       silentQuery(client, 'COMMIT', [], function() {
         done();
-        var toSend = results[3];
+        var toSend = results[4];
         cb(null, toSend);
       });
     });