diff --git a/.upgradenotes/MDL-82687-2024080211282638.yml b/.upgradenotes/MDL-82687-2024080211282638.yml
new file mode 100644
index 00000000000..19dc08a008b
--- /dev/null
+++ b/.upgradenotes/MDL-82687-2024080211282638.yml
@@ -0,0 +1,10 @@
+issueNumber: MDL-82687
+notes:
+  core_form:
+    - message:
+        Previously, the 'duration' form field type would allow users to input positive or negative durations.
+        However looking at all the uses, everyone was expecting this input type to only accept times >= 0 seconds,
+        and almost no-one was bothering to write manual form validation, leading to subtle bugs.
+        So now, by default this field type will validate the input value is not negative. If you need the
+        previous behaviour, there is a new option 'allownegative' which you can set to true. (The default is false.)
+      type: improved
diff --git a/lang/en/form.php b/lang/en/form.php
index d4304482b5c..123ff4d5076 100644
--- a/lang/en/form.php
+++ b/lang/en/form.php
@@ -39,6 +39,7 @@ $string['err_minlength'] = 'You must enter at least {$a->format} characters here
 $string['err_nonzero'] = 'You must enter a number not starting with a 0 here.';
 $string['err_nopunctuation'] = 'You must enter no punctuation characters here.';
 $string['err_numeric'] = 'You must enter a number here.';
+$string['err_positiveduration'] = 'This duration cannot be negative.';
 $string['err_positiveint'] = 'You must enter a whole number that is greater than 0.';
 $string['err_rangelength'] = 'You must enter between {$a->format[0]} and {$a->format[1]} characters here.';
 $string['err_required'] = 'You must supply a value here.';
diff --git a/lib/form/duration.php b/lib/form/duration.php
index 0ff1aaf2ee2..e6a7e8319a2 100644
--- a/lib/form/duration.php
+++ b/lib/form/duration.php
@@ -36,6 +36,9 @@ require_once($CFG->libdir . '/form/text.php');
  * HTML class for a length of time. For example, 30 minutes of 4 days. The
  * values returned to PHP is the duration in seconds (an int rounded to the nearest second).
  *
+ * By default, only durations >= 0 can be input. If you want to allow negative
+ * durations set the option allownegative.
+ *
  * @package   core_form
  * @category  form
  * @copyright 2009 Tim Hunt
@@ -46,9 +49,10 @@ class MoodleQuickForm_duration extends MoodleQuickForm_group {
      * Control the field names for form elements
      * optional => if true, show a checkbox beside the element to turn it on (or off)
      * defaultunit => which unit is default when the form is blank (default Minutes).
+     * allownegative => are durations < 0 allowed? (default false)
      * @var array
      */
-    protected $_options = ['optional' => false, 'defaultunit' => MINSECS];
+    protected $_options = ['optional' => false, 'defaultunit' => MINSECS, 'allownegative' => false];
 
     /** @var array associative array of time units (days, hours, minutes, seconds) */
     private $_units = null;
@@ -64,6 +68,7 @@ class MoodleQuickForm_duration extends MoodleQuickForm_group {
     *              the time is blank. If not specified, minutes is used.
     *      'units' => array containing some or all of 1, MINSECS, HOURSECS, DAYSECS and WEEKSECS
     *              which unit choices to offer.
+    *      'allownegative' => true/false - are durations < 0 allowed? (default false)
     * @param mixed $attributes Either a typical HTML attribute string or an associative array
     */
     public function __construct($elementName = null, $elementLabel = null,
@@ -78,6 +83,7 @@ class MoodleQuickForm_duration extends MoodleQuickForm_group {
             $options = [];
         }
         $this->_options['optional'] = !empty($options['optional']);
+        $this->_options['allownegative'] = !empty($options['allownegative']);
         if (isset($options['defaultunit'])) {
             if (!array_key_exists($options['defaultunit'], $this->get_units())) {
                 throw new coding_exception($options['defaultunit'] .
@@ -248,6 +254,14 @@ class MoodleQuickForm_duration extends MoodleQuickForm_group {
         }
     }
 
+    #[\Override]
+    public function validateSubmitValue($values) {
+        if ($this->exportValue($values) < 0 && !$this->_options['allownegative']) {
+            return get_string('err_positiveduration', 'core_form');
+        }
+        return null;
+    }
+
     /**
      * Returns HTML for advchecbox form element.
      *
diff --git a/lib/form/tests/duration_test.php b/lib/form/tests/duration_test.php
index 5158f8f6391..2dd27de07ad 100644
--- a/lib/form/tests/duration_test.php
+++ b/lib/form/tests/duration_test.php
@@ -14,17 +14,6 @@
 // You should have received a copy of the GNU General Public License
 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 
-/**
- * Unit tests for MoodleQuickForm_duration
- *
- * Contains test cases for testing MoodleQuickForm_duration
- *
- * @package    core_form
- * @category   test
- * @copyright  2009 Tim Hunt
- * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
- */
-
 namespace core_form;
 
 use moodleform;
@@ -44,6 +33,7 @@ require_once($CFG->libdir . '/form/duration.php');
  * @category   test
  * @copyright  2009 Tim Hunt
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @covers     \MoodleQuickForm_duration
  */
 class duration_test extends \basic_testcase {
 
@@ -54,7 +44,7 @@ class duration_test extends \basic_testcase {
      */
     protected function get_test_form(): MoodleQuickForm {
         $form = new temp_form_duration();
-        return $form->getform();
+        return $form->get_form();
     }
 
     /**
@@ -192,6 +182,47 @@ class duration_test extends \basic_testcase {
         $this->assertEquals(['testel' => $expected], $el->exportValue($values, true));
         $this->assertEquals($expected, $el->exportValue($values));
     }
+
+    /**
+     * Test cases for {@see test_validate_submit_value_negative_blocked()}.
+     * @return array[] test cases.
+     */
+    public static function validate_submit_value_cases(): array {
+        return [
+            [false, -10, MINSECS, false],
+            [false, 10, MINSECS, true],
+            [false, 0, MINSECS, true],
+            [true, -10, MINSECS, true],
+            [true, 10, MINSECS, true],
+            [true, 0, MINSECS, true],
+        ];
+    }
+
+    /**
+     * Test for {@see MoodleQuickForm_duration::validateSubmitValue()}.
+     *
+     * @dataProvider validate_submit_value_cases
+     * @param bool $allownegative whether the element should be created to allow negative values.
+     * @param int $number the number submitted.
+     * @param int $unit the unit submitted.
+     * @param bool $isvalid whether this submission is valid.
+     */
+    public function test_validate_submit_value(bool $allownegative, int $number, int $unit, bool $isvalid): void {
+        $form = new temp_form_duration(null, null, 'post', '', null, true);
+        /** @var \MoodleQuickForm_duration $element */
+        $element = $form->get_form()->addElement('duration', 'testel', '', ['allownegative' => $allownegative]);
+
+        $values = ['testel' => ['number' => $number, 'timeunit' => $unit]];
+
+        if ($isvalid) {
+            $this->assertNull($element->validateSubmitValue($values));
+        } else {
+            $this->assertEquals(
+                get_string('err_positiveduration', 'core_form'),
+                $element->validateSubmitValue($values),
+            );
+        }
+    }
 }
 
 /**
@@ -209,7 +240,7 @@ class temp_form_duration extends moodleform {
      * Returns form reference
      * @return MoodleQuickForm
      */
-    public function getform() {
+    public function get_form() {
         $mform = $this->_form;
         // Set submitted flag, to simulate submission.
         $mform->_flagSubmitted = true;
diff --git a/mod/quiz/tests/behat/settings_form_validation.feature b/mod/quiz/tests/behat/settings_form_validation.feature
new file mode 100644
index 00000000000..974f99aee8c
--- /dev/null
+++ b/mod/quiz/tests/behat/settings_form_validation.feature
@@ -0,0 +1,28 @@
+@mod @mod_quiz
+Feature: Settings form fields are validated
+  To help me avoid mistakes
+  As a teacher
+  I need the quiz settings to be validated
+
+  Background:
+    Given the following "users" exist:
+      | username | firstname |
+      | teacher  | Teach     |
+    And the following "courses" exist:
+      | fullname | shortname | category |
+      | Course 1 | C1        | 0        |
+    And the following "course enrolments" exist:
+      | user     | course | role           |
+      | teacher  | C1     | editingteacher |
+    And the following "activities" exist:
+      | activity | course | section | name        |
+      | quiz     | C1     | 1       | Test quiz 1 |
+
+  Scenario: Negative time limits are not allowed
+    When I am on the "Test quiz 1" "quiz activity editing" page logged in as teacher
+    And I expand all fieldsets
+    And I set the following fields to these values:
+      | id_timelimit_enabled | 1   |
+      | id_timelimit_number  | -10 |
+    And I press "Save and display"
+    Then I should see "This duration cannot be negative"