diff --git a/addons/point_of_sale/res_users.py b/addons/point_of_sale/res_users.py
index d2d4cef9a09..4aef0ad909e 100644
--- a/addons/point_of_sale/res_users.py
+++ b/addons/point_of_sale/res_users.py
@@ -12,3 +12,13 @@ class res_users(osv.osv):
         'pos_security_pin': fields.char('Security PIN',size=32, help='A Security PIN used to protect sensible functionality in the Point of Sale'),
         'pos_config' : fields.many2one('pos.config', 'Default Point of Sale', domain=[('state', '=', 'active')]),
     }
+
+    def _check_pin(self, cr, uid, ids, context=None):
+        for user in self.browse(cr, uid, ids, context=context):
+            if user.pos_security_pin and not user.pos_security_pin.isdigit():
+                return False
+        return True
+
+    _constraints = [
+        (_check_pin, "Security PIN can only contain digits",['pos_security_pin']),
+    ]