diff --git a/mod/quiz/comment.php b/mod/quiz/comment.php
index e6b748b00c2..37ef4d9a62d 100644
--- a/mod/quiz/comment.php
+++ b/mod/quiz/comment.php
@@ -72,6 +72,9 @@ $summary->add_item('quizname', get_string('modulename', 'quiz'), format_string($
 // Question name.
 $summary->add_item('questionname', get_string('question', 'quiz'), $attemptobj->get_question_name($slot));
 
+// Error message in case of input invalid mark.
+$submiterror = false;
+
 // Process any data that was submitted.
 if (data_submitted() && confirm_sesskey()) {
     if (optional_param('submit', false, PARAM_BOOL) && question_engine::is_manual_grade_in_range($attemptobj->get_uniqueid(), $slot)) {
@@ -96,12 +99,18 @@ if (data_submitted() && confirm_sesskey()) {
         echo $output->notification(get_string('changessaved'), 'notifysuccess');
         close_window(2, true);
         die;
+    } else {
+        $submiterror = true;
     }
 }
 
 // Print quiz information.
 echo html_writer::div($output->render($summary), 'mb-3');
 
+// Display notification if current mark is invalid.
+if ($submiterror) {
+    echo $output->notification(get_string('savemanualgradingfailed', 'quiz'), \core\output\notification::NOTIFY_ERROR);
+}
 // Print the comment form.
 echo '<form method="post" class="mform" id="manualgradingform" action="' .
         $CFG->wwwroot . '/mod/quiz/comment.php">';
diff --git a/mod/quiz/lang/en/quiz.php b/mod/quiz/lang/en/quiz.php
index de617c2477d..64e9656a09c 100644
--- a/mod/quiz/lang/en/quiz.php
+++ b/mod/quiz/lang/en/quiz.php
@@ -967,6 +967,7 @@ $string['saveandedit'] = 'Save changes and edit questions';
 $string['saveattemptfailed'] = 'Failed to save the current quiz attempt.';
 $string['savedfromdeletedcourse'] = 'Saved from deleted course "{$a}"';
 $string['savegrades'] = 'Save grades';
+$string['savemanualgradingfailed'] = 'Modification not saved. Please check the message below and try again.';
 $string['savemyanswers'] = 'Save my answers';
 $string['savenosubmit'] = 'Save without submitting';
 $string['saveoverrideandstay'] = 'Save and enter another override';
diff --git a/question/behaviour/rendererbase.php b/question/behaviour/rendererbase.php
index 21de819f65c..9ebb9ece7b3 100644
--- a/question/behaviour/rendererbase.php
+++ b/question/behaviour/rendererbase.php
@@ -164,7 +164,7 @@ abstract class qbehaviour_renderer extends plugin_renderer_base {
             $error = $qa->validate_manual_mark($currentmark);
             $errorclass = '';
             if ($error !== '') {
-                $erroclass = ' error';
+                $errorclass = ' error alert-danger';
                 $error = html_writer::tag('span', $error,
                         array('class' => 'error')) . html_writer::empty_tag('br');
             }