diff --git a/mod/workshop/form/numerrors/assessment_form.php b/mod/workshop/form/numerrors/assessment_form.php
index 37babb8a4d9f2..90ec66f66e268 100644
--- a/mod/workshop/form/numerrors/assessment_form.php
+++ b/mod/workshop/form/numerrors/assessment_form.php
@@ -71,9 +71,11 @@ protected function definition_inner(&$mform) {
 
             // evaluation of the assertion
             $label = get_string('dimensiongrade', 'workshopform_numerrors');
-            $mform->addElement('radio', 'grade__idx_' . $i, get_string('yourassessment', 'workshop'), $fields->{'grade0__idx_'.$i}, 0);
-            $mform->addElement('radio', 'grade__idx_' . $i, '', $fields->{'grade1__idx_'.$i}, 1);
-            $mform->setDefault('grade__idx_' . $i, 0);
+            $mform->addGroup(array(
+                $mform->createElement('radio', 'grade__idx_' . $i, '', $fields->{'grade0__idx_'.$i}, -1),
+                $mform->createElement('radio', 'grade__idx_' . $i, '', $fields->{'grade1__idx_'.$i}, 1),
+            ), 'group_grade__idx_' . $i, get_string('yourassessment', 'workshop'), '<br />', false);
+            $mform->addRule('group_grade__idx_' . $i, get_string('required'), 'required');
 
             // comment
             $label = get_string('dimensioncomment', 'workshopform_numerrors');
diff --git a/mod/workshop/form/numerrors/lib.php b/mod/workshop/form/numerrors/lib.php
index f1acce27b0a0f..8abe992086c12 100644
--- a/mod/workshop/form/numerrors/lib.php
+++ b/mod/workshop/form/numerrors/lib.php
@@ -252,7 +252,7 @@ public function get_assessment_form(moodle_url $actionurl=null, $mode='preview',
                 $dimid = $fields->{'dimensionid__idx_'.$i};
                 if (isset($grades[$dimid])) {
                     $current->{'gradeid__idx_'.$i}      = $grades[$dimid]->id;
-                    $current->{'grade__idx_'.$i}        = $grades[$dimid]->grade;
+                    $current->{'grade__idx_'.$i}        = ($grades[$dimid]->grade == 0 ? -1 : 1);
                     $current->{'peercomment__idx_'.$i}  = $grades[$dimid]->peercomment;
                 }
             }
@@ -294,7 +294,7 @@ public function save_assessment(stdclass $assessment, stdclass $data) {
             $grade->assessmentid        = $assessment->id;
             $grade->strategy            = 'numerrors';
             $grade->dimensionid         = $data->{'dimensionid__idx_' . $i};
-            $grade->grade               = $data->{'grade__idx_' . $i};
+            $grade->grade               = ($data->{'grade__idx_' . $i} <= 0 ? 0 : 1);
             $grade->peercomment         = $data->{'peercomment__idx_' . $i};
             $grade->peercommentformat   = FORMAT_HTML;
             if (empty($grade->id)) {