diff --git a/public/question/behaviour/deferredcbm/behaviourtype.php b/public/question/behaviour/deferredcbm/behaviourtype.php
index 254e863f51d..8e5e0aba6b5 100644
--- a/public/question/behaviour/deferredcbm/behaviourtype.php
+++ b/public/question/behaviour/deferredcbm/behaviourtype.php
@@ -48,7 +48,8 @@ class qbehaviour_deferredcbm_type extends qbehaviour_deferredfeedback_type {
         }
 
         // Prepare accumulators to hold the data we are about to collect.
-        $notansweredcount  = 0;
+        $totalquestions = 0;
+        $notansweredcount = 0;
         $notansweredweight = 0;
         $attemptcount = array(
             question_cbm::HIGH => 0,
@@ -76,6 +77,7 @@ class qbehaviour_deferredcbm_type extends qbehaviour_deferredfeedback_type {
             if (strpos($qa->get_behaviour_name(), 'cbm') === false || $qa->get_max_mark() < 0.0000005) {
                 continue;
             }
+            $totalquestions += 1;
 
             $gradedstep = $qa->get_last_step_with_behaviour_var('_rawfraction');
 
@@ -100,8 +102,12 @@ class qbehaviour_deferredcbm_type extends qbehaviour_deferredfeedback_type {
             $totalcbmscore[$certainty] += $qa->get_mark();
         }
 
+        // Did we find any CBM questions? If not, just quit here.
+        if ($totalquestions === 0) {
+            return $summarydata;
+        }
+
         // Hence compute some statistics.
-        $totalquestions   = $notansweredcount + array_sum($attemptcount);
         $grandtotalweight = $notansweredweight + array_sum($totalweight);
         $accuracy         = array_sum($totalrawscore) / $grandtotalweight;
         $averagecbm       = array_sum($totalcbmscore) / $grandtotalweight;
diff --git a/public/question/behaviour/deferredcbm/tests/behaviour_type_test.php b/public/question/behaviour/deferredcbm/tests/behaviour_type_test.php
index 8256241a9e3..0d11851083f 100644
--- a/public/question/behaviour/deferredcbm/tests/behaviour_type_test.php
+++ b/public/question/behaviour/deferredcbm/tests/behaviour_type_test.php
@@ -134,6 +134,29 @@ final class behaviour_type_test extends \qbehaviour_walkthrough_test_base {
                 $summarydata['qbehaviour_cbm_judgement1']['content']);
     }
 
+    /**
+     * Test that CBM summary is not shown when there are no CBM questions in the attempt.
+     * @covers \qbehaviour_deferredcbm_type::summarise_usage
+     */
+    public function test_summarise_usage_no_cbm_questions(): void {
+        // Create a usage comprising 2 essay questions.
+        $this->quba->set_preferred_behaviour('deferredcbm');
+        $this->quba->add_question(\test_question_maker::make_an_essay_question(), 1);
+        $this->quba->add_question(\test_question_maker::make_an_essay_question(), 1);
+        $this->quba->start_all_questions();
+
+        // Process responses right, high certainty; right, med certainty; wrong, med certainty.
+        $this->quba->process_action(1, ['answer' => 'essay answer1', 'answerformat' => FORMAT_PLAIN]);
+        $this->quba->process_action(2, ['answer' => 'essay answer2', 'answerformat' => FORMAT_PLAIN]);
+        $this->quba->finish_all_questions();
+
+        // Get the summary.
+        $summarydata = $this->quba->get_summary_information(new question_display_options());
+
+        // Verify that there is no CBM summary.
+        $this->assertArrayNotHasKey('qbehaviour_cbm_entire_quiz_heading', $summarydata);
+    }
+
     public function test_calculate_bonus(): void {
         $this->assertEqualsWithDelta(0.05,  $this->behaviourtype->calculate_bonus(1, 1 / 2), question_testcase::GRADE_DELTA);
         $this->assertEqualsWithDelta(-0.01, $this->behaviourtype->calculate_bonus(2, 9 / 10), question_testcase::GRADE_DELTA);