diff --git a/mod/quiz/report/overview/overview_table.php b/mod/quiz/report/overview/overview_table.php
index 2e1bb0629fc..0cbbfecdd30 100644
--- a/mod/quiz/report/overview/overview_table.php
+++ b/mod/quiz/report/overview/overview_table.php
@@ -57,16 +57,18 @@ class quiz_report_overview_table extends table_sql {
                 $this->add_data_keyed($groupaveragerow);
             }
 
-            list($s_usql, $s_params) = $DB->get_in_or_equal($this->students);
-            $overallaverage = $DB->get_record_sql($averagesql." AND qg.userid $s_usql", array_merge($params, $s_params));
-            $overallaveragerow = array($namekey => get_string('overallaverage', 'grades'),
-                        'sumgrades' => quiz_format_grade($this->quiz, $overallaverage->grade),
-                        'feedbacktext'=> strip_tags(quiz_report_feedback_for_grade($overallaverage->grade, $this->quiz->id, $this->context)));
-            if($this->detailedmarks && ($this->qmsubselect || $this->quiz->attempts == 1)) {
-                $avggradebyq = quiz_get_average_grade_for_questions($this->quiz, $this->students);
-                $overallaveragerow += quiz_format_average_grade_for_questions($avggradebyq, $this->questions, $this->quiz, $this->is_downloading());
+            if ($this->students) {
+                list($s_usql, $s_params) = $DB->get_in_or_equal($this->students);
+                $overallaverage = $DB->get_record_sql($averagesql." AND qg.userid $s_usql", array_merge($params, $s_params));
+                $overallaveragerow = array($namekey => get_string('overallaverage', 'grades'),
+                            'sumgrades' => quiz_format_grade($this->quiz, $overallaverage->grade),
+                            'feedbacktext'=> strip_tags(quiz_report_feedback_for_grade($overallaverage->grade, $this->quiz->id, $this->context)));
+                if($this->detailedmarks && ($this->qmsubselect || $this->quiz->attempts == 1)) {
+                    $avggradebyq = quiz_get_average_grade_for_questions($this->quiz, $this->students);
+                    $overallaveragerow += quiz_format_average_grade_for_questions($avggradebyq, $this->questions, $this->quiz, $this->is_downloading());
+                }
+                $this->add_data_keyed($overallaveragerow);
             }
-            $this->add_data_keyed($overallaveragerow);
         }
     }