diff --git a/php/libraries/NDB_BVL_Instrument.class.inc b/php/libraries/NDB_BVL_Instrument.class.inc
index 83066c59ee2..17f4ef76770 100644
--- a/php/libraries/NDB_BVL_Instrument.class.inc
+++ b/php/libraries/NDB_BVL_Instrument.class.inc
@@ -1813,7 +1813,8 @@ abstract class NDB_BVL_Instrument extends NDB_Page
                 "dnk"          => "DNK",
                 "refusal"      => "Refusal",
                 'not_answered' => 'Not Answered',
-            ]
+            ],
+            ['class' => 'form-control input-sm not-answered']
         );
         $this->addGroup($group, $field . "_group", $label, '');
         $this->XINRegisterRule(
diff --git a/test/unittests/NDB_BVL_Instrument_Test.php b/test/unittests/NDB_BVL_Instrument_Test.php
index a17f9b541df..6e9bc39499f 100644
--- a/test/unittests/NDB_BVL_Instrument_Test.php
+++ b/test/unittests/NDB_BVL_Instrument_Test.php
@@ -458,7 +458,7 @@ function testAddHourMinElement()
                     ],
                     ['label' => '',
                         'name'    => 'hourMinField_status',
-                        'class'   => 'form-control input-sm',
+                        'class'   => 'form-control input-sm not-answered',
                         'type'    => 'select',
                         'options' => [
                             ''             => '',
@@ -472,7 +472,7 @@ function testAddHourMinElement()
                 ],
                 'label'     => 'hourMinLabel',
                 'delimiter' => ' ',
-                'options'   => false,
+                'options'   => null,
                 'html'      => $this->_instrument->form->groupHTML($groupEl)
             ]
         );