diff --git a/lib/main.js b/lib/main.js
index bde0a895..c10751a8 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -567,13 +567,15 @@ Lambda.prototype._buildAndArchive = function (program, archiveCallback) {
   })
 }
 
-Lambda.prototype._listEventSourceMappings = function (lambda, params, cb) {
-  return lambda.listEventSourceMappings(params, function (err, data) {
-    var eventSourceMappings = []
-    if (!err && data && data.EventSourceMappings) {
-      eventSourceMappings = data.EventSourceMappings
-    }
-    return cb(err, eventSourceMappings)
+Lambda.prototype._listEventSourceMappings = (lambda, params) => {
+  return new Promise((resolve, reject) => {
+    lambda.listEventSourceMappings(params, (err, data) => {
+      if (err) return reject(err)
+      if (data && data.EventSourceMappings) {
+        return resolve(data.EventSourceMappings)
+      }
+      return resolve([])
+    })
   })
 }
 
@@ -768,11 +770,9 @@ Lambda.prototype._deployToRegion = function (program, params, region) {
       'FunctionName': params.FunctionName
     }).promise().then(() => {
       // Function exists
-      _this._listEventSourceMappings(lambda, {
+      return _this._listEventSourceMappings(lambda, {
         'FunctionName': params.FunctionName
-      }, (err, existingEventSourceList) => {
-        if (err) return reject(err)
-
+      }).then((existingEventSourceList) => {
         return Promise.all([
           _this._uploadExisting(lambda, params).then((results) => {
             console.log('=> Zip file(s) done uploading. Results follow: ')
@@ -791,9 +791,9 @@ Lambda.prototype._deployToRegion = function (program, params, region) {
           )
         ]).then((results) => {
           resolve(results)
-        }).catch((err) => {
-          reject(err)
         })
+      }).catch((err) => {
+        reject(err)
       })
     }).catch(() => {
       // Function does not exist
@@ -815,8 +815,6 @@ Lambda.prototype._deployToRegion = function (program, params, region) {
           )
         ]).then((results) => {
           resolve(results)
-        }).catch((err) => {
-          reject(err)
         })
       }).catch((err) => {
         reject(err)
diff --git a/test/main.js b/test/main.js
index 4314d992..5c51f4f7 100644
--- a/test/main.js
+++ b/test/main.js
@@ -800,6 +800,20 @@ describe('lib/main', function () {
     })
   })
 
+  describe('_listEventSourceMappings', () => {
+    it('simple test with mock', () => {
+      return lambda._listEventSourceMappings(
+        awsLambda,
+        { FunctionName: 'test-func' }
+      ).then((results) => {
+        assert.deepEqual(
+          results,
+          lambdaMockSettings.listEventSourceMappings.EventSourceMappings
+        )
+      })
+    })
+  })
+
   describe('_updateEventSources', () => {
     const eventSourcesJsonValue = {
       EventSourceMappings: [{