diff --git a/addons/web/static/tests/core/widget_tests.js b/addons/web/static/tests/core/widget_tests.js
index 9510079e380..f61d4a18f9b 100644
--- a/addons/web/static/tests/core/widget_tests.js
+++ b/addons/web/static/tests/core/widget_tests.js
@@ -391,7 +391,9 @@ QUnit.module('core', {}, function () {
                     return def;
                 },
             },
-            services: [AjaxService],
+            services: {
+                ajax: AjaxService
+            },
         });
         var widget = new Widget(parent);
 
diff --git a/addons/web/static/tests/helpers/test_utils.js b/addons/web/static/tests/helpers/test_utils.js
index 7c47bf5574a..5bf8e3d2e1b 100644
--- a/addons/web/static/tests/helpers/test_utils.js
+++ b/addons/web/static/tests/helpers/test_utils.js
@@ -494,7 +494,7 @@ function addMockEnvironment(widget, params) {
     // Dispatch service calls
     // Note: some services could call other services at init,
     // Which is why we have to init services after that
-    var services = {ajax: null}; // mocked ajax service already loaded
+    var services = {};
     intercept(widget, 'call_service', function (ev) {
         var args, result;
         if (services[ev.data.service]) {
@@ -502,7 +502,7 @@ function addMockEnvironment(widget, params) {
             args = (ev.data.args || []);
             result = service[ev.data.method].apply(service, args);
         } else if (ev.data.service === 'ajax') {
-            // ajax service is already mocked by the server
+            // use ajax service that is mocked by the server
             var route = ev.data.args[0];
             args = ev.data.args[1];
             result = mockServer.performRpc(route, args);
@@ -560,6 +560,9 @@ function addMockEnvironment(widget, params) {
     // Deploy services
     var done = false;
     var servicesToDeploy = _.clone(params.services);
+    if (!servicesToDeploy.ajax) {
+        services.ajax = null; // use mocked ajax from mocked server
+    }
     while (!done) {
         var serviceName = _.findKey(servicesToDeploy, function (Service) {
             return !_.some(Service.prototype.dependencies, function (depName) {