diff --git a/accountant/frontend/static/js/accounts.js b/accountant/frontend/static/js/accounts.js
index c103df1..5e63943 100644
--- a/accountant/frontend/static/js/accounts.js
+++ b/accountant/frontend/static/js/accounts.js
@@ -15,6 +15,7 @@
     along with Accountant.  If not, see <http://www.gnu.org/licenses/>.
  */
 // vim: set tw=80 ts=2 sw=2 sts=2:
+'use strict';
 
 accountantApp
 
diff --git a/accountant/frontend/static/js/app.js b/accountant/frontend/static/js/app.js
index 7ac207c..e5b52a3 100644
--- a/accountant/frontend/static/js/app.js
+++ b/accountant/frontend/static/js/app.js
@@ -14,6 +14,8 @@
     You should have received a copy of the GNU Affero General Public License
     along with Accountant.  If not, see <http://www.gnu.org/licenses/>.
  */
+'use strict';
+
 var accountantApp = angular.module("accountantApp", [
     'ngResource', 'ngRoute',
     'mgcrea.ngStrap',
diff --git a/accountant/frontend/static/js/operations.js b/accountant/frontend/static/js/operations.js
index a787063..4ba0213 100644
--- a/accountant/frontend/static/js/operations.js
+++ b/accountant/frontend/static/js/operations.js
@@ -15,6 +15,8 @@
     along with Accountant.  If not, see <http://www.gnu.org/licenses/>.
  */
 // vim: set tw=80 ts=2 sw=2 sts=2:
+'use strict';
+
 accountantApp
 
 .factory("Operation", [ "$resource", function($resource)  {
diff --git a/accountant/frontend/static/js/scheduler.js b/accountant/frontend/static/js/scheduler.js
index 8cb312d..1bb544e 100644
--- a/accountant/frontend/static/js/scheduler.js
+++ b/accountant/frontend/static/js/scheduler.js
@@ -14,6 +14,8 @@
     You should have received a copy of the GNU Affero General Public License
     along with Accountant.  If not, see <http://www.gnu.org/licenses/>.
  */
+'use strict';
+
 accountantApp
 
 .factory("ScheduledOperation", ["$resource", function($resource) {