diff --git a/src/js/client.js b/src/js/client.js
index a791a4eb1..01151fd51 100644
--- a/src/js/client.js
+++ b/src/js/client.js
@@ -1721,6 +1721,15 @@ angular.module('Application').service('Client', ['$http', '$interval', '$timeout
         });
     };
 
+    Client.prototype.getDNSRecords = function (domain, subdomain, type, callback) {
+        get('/api/v1/domains/' + domain + '/dns?subdomain=' + subdomain + '&type=' + type, null, function (error, data, status) {
+            if (error) return callback(error);
+            if (status !== 200) return callback(new ClientError(status, data));
+
+            callback(null, data.values);
+        });
+    };
+
     Client.prototype.addMailDomain = function (domain, callback) {
         post('/api/v1/mail', { domain: domain }, null, function (error, data, status) {
             if (error) return callback(error);
diff --git a/src/views/app.html b/src/views/app.html
index 21f416f47..b4d0238d5 100644
--- a/src/views/app.html
+++ b/src/views/app.html
@@ -81,6 +81,28 @@
   </div>
 </div>
 
+<!-- Modal domain collision -->
+<div class="modal fade" id="domainCollisionsModal" tabindex="-1" role="dialog">
+    <div class="modal-dialog">
+      <div class="modal-content">
+          <div class="modal-header">
+            <h4 class="modal-title">Domain Collision</h4>
+          </div>
+        <div class="modal-body">
+          <p>By default Cloudron does not overwrite DNS records which exist outside of Cloudron.</p>
+          <p>The following domains already exist outside of Cloudron:</p>
+          <ul>
+            <li ng-repeat="domain in location.domainCollisions">{{ domain.subdomain + '.' + domain.domain }}</li>
+          </ul>
+        </div>
+        <div class="modal-footer">
+          <button type="button" class="btn btn-default" data-dismiss="modal">Cancel</button>
+          <button type="button" class="btn btn-danger" ng-click="location.submit(true)">Overwrite existing DNS Records</button>
+        </div>
+      </div>
+    </div>
+  </div>
+
 <!-- Modal update app -->
 <div class="modal fade" id="updateModal" tabindex="-1" role="dialog">
   <div class="modal-dialog">
diff --git a/src/views/app.js b/src/views/app.js
index 9eb3e2b15..87f10449d 100644
--- a/src/views/app.js
+++ b/src/views/app.js
@@ -3,6 +3,7 @@
 /* global angular */
 /* global $ */
 /* global asyncSeries */
+/* global asyncForEach */
 
 
 // TODO use this once we enable custom SSL certificate ui again
@@ -156,7 +157,7 @@ angular.module('Application').controller('AppController', ['$scope', '$location'
     $scope.location = {
         busy: false,
         error: {},
-        success: false,
+        domainCollisions: [],
 
         domain: null,
         location: '',
@@ -182,6 +183,7 @@ angular.module('Application').controller('AppController', ['$scope', '$location'
             var app = $scope.app;
 
             $scope.location.error = {};
+            $scope.location.domainCollisions = [];
             $scope.location.location = app.location;
             $scope.location.domain = $scope.domains.filter(function (d) { return d.domain === app.domain; })[0];
             $scope.location.portBindingsInfo = angular.extend({}, app.manifest.tcpPorts, app.manifest.udpPorts); // Portbinding map only for information
@@ -199,9 +201,12 @@ angular.module('Application').controller('AppController', ['$scope', '$location'
             }
         },
 
-        submit: function () {
+        submit: function (overwriteDns) {
+            $('#domainCollisionsModal').modal('hide');
+
             $scope.location.busy = true;
             $scope.location.error = {};
+            $scope.location.domainCollisions = [];
 
             // only use enabled ports from portBindings
             var portBindings = {};
@@ -212,30 +217,62 @@ angular.module('Application').controller('AppController', ['$scope', '$location'
             }
 
             var data = {
+                overwriteDns: !!overwriteDns,
                 location: $scope.location.location,
                 domain: $scope.location.domain.domain,
                 portBindings: portBindings,
                 alternateDomains: $scope.location.alternateDomains.map(function (a) { return { subdomain: a.subdomain, domain: a.domain.domain };})
             };
 
-            Client.configureApp($scope.app.id, 'location', data, function (error) {
-                if (error && (error.statusCode === 409 || error.statusCode === 400)) {
-                    if ((error.location && error.domain) || error.field === 'location') {
-                        $scope.location.error.location = error.message;
-                        $scope.locationForm.$setPristine();
-                    } else {
-                        $scope.location.error.alternateDomains = error.message;
-                    }
+            // pre-flight only for changed domains
+            var domains = [];
+            if ($scope.app.domain !== data.domain || $scope.app.location !== data.location) domains.push({ subdomain: data.location, domain: data.domain });
+            data.alternateDomains.forEach(function (a) {
+                if ($scope.app.alternateDomains.some(function (d) { return d.domain === a.domain && d.subdomain === a.subdomain; })) return;
+                domains.push({ subdomain: a.subdomain, domain: a.domain });
+            });
 
+            asyncForEach(domains, function (domain, callback) {
+                if (overwriteDns) return callback();
+
+                Client.getDNSRecords(domain.domain, domain.subdomain, 'A', function (error, result) {
+                    // TODO handle credential errors
+                    if (error) return callback(error);
+
+                    if (result.length) $scope.location.domainCollisions.push(domain);
+
+                    callback();
+                });
+            }, function (error) {
+                if (error) {
                     $scope.location.busy = false;
-                    return;
+                    return Client.error(error);
                 }
-                if (error) return Client.error(error);
 
-                $scope.location.success = true;
-                $scope.location.busy = false;
+                if ($scope.location.domainCollisions.length) {
+                    $scope.location.busy = false;
+                    return $('#domainCollisionsModal').modal('show');
+                }
 
-                refreshApp();
+                Client.configureApp($scope.app.id, 'location', data, function (error) {
+                    if (error && (error.statusCode === 409 || error.statusCode === 400)) {
+                        if ((error.location && error.domain) || error.field === 'location') {
+                            $scope.location.error.location = error.message;
+                            $scope.locationForm.$setPristine();
+                        } else {
+                            $scope.location.error.alternateDomains = error.message;
+                        }
+
+                        $scope.location.busy = false;
+                        return;
+                    }
+                    if (error) return Client.error(error);
+
+                    $scope.locationForm.$setPristine();
+                    $scope.location.busy = false;
+
+                    refreshApp();
+                });
             });
         }
     };