diff --git a/question/classes/statistics/questions/calculated_question_summary.php b/question/classes/statistics/questions/calculated_question_summary.php
index 982baf347af..bbce6db836d 100644
--- a/question/classes/statistics/questions/calculated_question_summary.php
+++ b/question/classes/statistics/questions/calculated_question_summary.php
@@ -23,8 +23,11 @@
  */
 
 namespace core_question\statistics\questions;
+
 defined('MOODLE_INTERNAL') || die();
 
+require_once($CFG->dirroot . '/question/engine/lib.php');
+
 /**
  * Class calculated_question_summary
  *
@@ -114,7 +117,7 @@ class calculated_question_summary extends calculated {
         $set = false;
 
         foreach ($this->subqstats as $subqstat) {
-            if (isset($subqstat->sd) && $subqstat->maxmark) {
+            if (isset($subqstat->sd) && $subqstat->maxmark > \question_utils::MARK_TOLERANCE) {
                 $value = $subqstat->sd / $subqstat->maxmark;
             } else {
                 $value = null;
diff --git a/question/tests/calculated_question_summary_test.php b/question/tests/calculated_question_summary_test.php
index 5717f1caf7a..b90dcf82366 100644
--- a/question/tests/calculated_question_summary_test.php
+++ b/question/tests/calculated_question_summary_test.php
@@ -127,7 +127,7 @@ class calculated_question_summary_test extends \advanced_testcase {
             ],
             'zero mark' => [
                 [
-                    (object)['questionid' => 1, 'sd' => 0.2, 'maxmark' => 0],
+                    (object)['questionid' => 1, 'sd' => 0, 'maxmark' => 0],
                     (object)['questionid' => 2, 'sd' => 0.1049, 'maxmark' => 1],
                 ],
                 [null, 0.1049]
@@ -139,6 +139,13 @@ class calculated_question_summary_test extends \advanced_testcase {
                 ],
                 [0.35, 0.4]
             ],
+            'zero max mark as loaded from the DB' => [
+                [
+                    (object)['questionid' => 1, 'sd' => '0.0000000000', 'maxmark' => '0.0000000'],
+                    (object)['questionid' => 2, 'sd' => '0.0000000000', 'maxmark' => '0.0000000'],
+                ],
+                [null, null]
+            ],
         ];
     }