diff --git a/mod/workshop/allocation/random/lib.php b/mod/workshop/allocation/random/lib.php
index 603cf36e18e..657d5228685 100644
--- a/mod/workshop/allocation/random/lib.php
+++ b/mod/workshop/allocation/random/lib.php
@@ -263,13 +263,17 @@ class workshop_random_allocator implements workshop_allocator {
      * @return array of integers
      */
     public static function available_numofreviews_list() {
-        $options = array();
-        $options[30] = 30;
-        $options[20] = 20;
-        $options[15] = 15;
-        for ($i = 10; $i >= 0; $i--) {
+
+        $options = [];
+
+        for ($i = 100; $i > 20; $i = $i - 10) {
             $options[$i] = $i;
         }
+
+        for ($i = 20; $i >= 0; $i--) {
+            $options[$i] = $i;
+        }
+
         return $options;
     }
 
diff --git a/mod/workshop/allocation/random/settings_form.php b/mod/workshop/allocation/random/settings_form.php
index b4798a72631..50fa1a2ec24 100644
--- a/mod/workshop/allocation/random/settings_form.php
+++ b/mod/workshop/allocation/random/settings_form.php
@@ -67,8 +67,8 @@ class workshop_random_allocator_form extends moodleform {
             workshop_random_allocator_setting::NUMPER_REVIEWER   => get_string('numperreviewer', 'workshopallocation_random')
         );
         $grpnumofreviews = array();
-        $grpnumofreviews[] = $mform->createElement('select', 'numofreviews', '',
-                workshop_random_allocator::available_numofreviews_list());
+        $grpnumofreviews[] = $mform->createElement('text', 'numofreviews', '', array('size' => 5, 'maxlength' => 20));
+        $mform->setType('numofreviews', PARAM_INT);
         $mform->setDefault('numofreviews', $plugindefaults->numofreviews);
         $grpnumofreviews[] = $mform->createElement('select', 'numper', '', $options_numper);
         $mform->setDefault('numper', workshop_random_allocator_setting::NUMPER_SUBMISSION);
@@ -98,4 +98,22 @@ class workshop_random_allocator_form extends moodleform {
 
         $this->add_action_buttons();
     }
+
+    /**
+     * Validate the allocation settings.
+     *
+     * @param array $data
+     * @param array $files
+     * @return array
+     */
+    public function validation($data, $files): array {
+
+        $errors = parent::validation($data, $files);
+
+        if ($data['numofreviews'] < 0) {
+            $errors['grpnumofreviews'] = get_string('invalidnum', 'core_error');
+        }
+
+        return $errors;
+    }
 }