diff --git a/question/behaviour/behaviourbase.php b/question/behaviour/behaviourbase.php
index d73328dbb49..65587851b10 100644
--- a/question/behaviour/behaviourbase.php
+++ b/question/behaviour/behaviourbase.php
@@ -388,7 +388,7 @@ abstract class question_behaviour {
 
         // So, now we know the comment is the same, so check the mark, if present.
         $previousfraction = $this->qa->get_fraction();
-        $newmark = $pendingstep->get_behaviour_var('mark');
+        $newmark = question_utils::clean_param_mark($pendingstep->get_behaviour_var('mark'));
 
         if (is_null($previousfraction)) {
             return is_null($newmark) || $newmark === '';
@@ -487,8 +487,7 @@ abstract class question_behaviour {
                 $fraction = null;
 
             } else {
-                $fraction = $pendingstep->get_behaviour_var('mark') /
-                        $pendingstep->get_behaviour_var('maxmark');
+                $fraction = $mark / $pendingstep->get_behaviour_var('maxmark');
                 if ($fraction > $this->qa->get_max_fraction() || $fraction < $this->qa->get_min_fraction()) {
                     throw new coding_exception('Score out of range when processing ' .
                             'a manual grading action.', 'Question ' . $this->question->id .
@@ -535,7 +534,7 @@ abstract class question_behaviour {
             $a->comment = '';
         }
 
-        $mark = $step->get_behaviour_var('mark');
+        $mark = question_utils::clean_param_mark($step->get_behaviour_var('mark'));
         if (is_null($mark) || $mark === '') {
             return get_string('commented', 'question', $a->comment);
         } else {
diff --git a/question/behaviour/manualgraded/tests/walkthrough_test.php b/question/behaviour/manualgraded/tests/walkthrough_test.php
index 95660479a1d..7eeb44b81a1 100644
--- a/question/behaviour/manualgraded/tests/walkthrough_test.php
+++ b/question/behaviour/manualgraded/tests/walkthrough_test.php
@@ -278,6 +278,54 @@ class qbehaviour_manualgraded_walkthrough_testcase extends qbehaviour_walkthroug
                 $qa->summarise_action($qa->get_last_step()));
     }
 
+    public function test_manual_graded_ignore_repeat_sumbission_commas() {
+        // Create an essay question.
+        $essay = test_question_maker::make_an_essay_question();
+        $this->start_attempt_at_question($essay, 'deferredfeedback', 10);
+
+        // Check the right model is being used.
+        $this->assertEquals('manualgraded', $this->quba->get_question_attempt(
+                $this->slot)->get_behaviour_name());
+
+        // Check the initial state.
+        $this->check_current_state(question_state::$todo);
+        $this->check_current_mark(null);
+
+        // Simulate some data submitted by the student.
+        $this->process_submission(array('answer' => 'This is my wonderful essay!', 'answerformat' => FORMAT_HTML));
+
+        // Verify.
+        $this->check_current_state(question_state::$complete);
+        $this->check_current_mark(null);
+
+        // Finish the attempt.
+        $this->quba->finish_all_questions();
+
+        // Verify.
+        $this->check_current_state(question_state::$needsgrading);
+        $this->check_current_mark(null);
+        $this->assertEquals('This is my wonderful essay!',
+                $this->quba->get_response_summary($this->slot));
+
+        // Now grade it with a mark with a comma.
+        $numsteps = $this->get_step_count();
+        $this->manual_grade('Pretty good!', '9,00000', FORMAT_HTML);
+        $this->check_step_count($numsteps + 1);
+        $this->check_current_state(question_state::$mangrpartial);
+        $this->check_current_mark(9);
+        $qa = $this->get_question_attempt();
+        $this->assertEquals('Manually graded 9 with comment: Pretty good!',
+                $qa->summarise_action($qa->get_last_step()));
+        $this->check_current_output(
+                new question_pattern_expectation('/' . preg_quote('Pretty good!', '/') . '/'));
+
+        // Process the same mark with a dot. Verify it does not add a new step.
+        $this->manual_grade('Pretty good!', '9.00000', FORMAT_HTML);
+        $this->check_step_count($numsteps + 1);
+        $this->check_current_state(question_state::$mangrpartial);
+        $this->check_current_mark(9);
+    }
+
     public function test_manual_graded_essay_can_grade_0() {
         global $PAGE;