diff --git a/lbplanner/classes/helpers/slot_helper.php b/lbplanner/classes/helpers/slot_helper.php
index 2083e989..f642ad53 100644
--- a/lbplanner/classes/helpers/slot_helper.php
+++ b/lbplanner/classes/helpers/slot_helper.php
@@ -285,10 +285,10 @@ public static function get_filters_for_slot(int $slotid): array {
      * NOTE: not taking into account time or fullness, only filters i.e. users' class and courses
      * TODO: replace $user with $vintage
      * @param slot[] $allslots the slots to filter
-     * @param mixed $user a user object - e.g. $USER or a user object from the database
+     * @param \stdClass $user a user object - e.g. $USER or a user object from the database
      * @return slot[] the filtered slot array
      */
-    public static function filter_slots_for_user(array $allslots, mixed $user): array {
+    public static function filter_slots_for_user(array $allslots, \stdClass $user): array {
         $mycourses = course_helper::get_all_lbplanner_courses();
         $mycourseids = [];
         foreach ($mycourses as $course) {
diff --git a/lbplanner/classes/model/slot.php b/lbplanner/classes/model/slot.php
index cff914bc..7408f9c8 100644
--- a/lbplanner/classes/model/slot.php
+++ b/lbplanner/classes/model/slot.php
@@ -28,6 +28,7 @@
 use local_lbplanner\enums\WEEKDAY;
 use local_lbplanner\helpers\slot_helper;
 
+use external_multiple_structure;
 use external_single_structure;
 use external_value;
 use moodle_exception;
@@ -68,6 +69,10 @@ class slot {
      * @var ?bool $forcuruser whether the current user has reserved this slot (gets filled in by helper functions)
      */
     private ?bool $forcuruser;
+    /**
+     * @var ?int[] $supervisors list of supervisors for this slot
+     */
+    private ?array $supervisors;
 
     /**
      * Constructs a new Slot
@@ -166,6 +171,25 @@ public function get_forcuruser(): bool {
         return $this->forcuruser;
     }
 
+    /**
+     * Returns the list of supervisor userIDs
+     *
+     * @return int[] this slot's supervsisors' userIDs
+     */
+    public function get_supervisors(): array {
+        global $DB;
+        if (is_null($this->supervisors)) {
+            $this->supervisors = $DB->get_records(
+                slot_helper::TABLE_SUPERVISORS,
+                ['slotid' => $this->id],
+                '',
+                ['userid']
+            );
+        }
+
+        return $this->supervisors;
+    }
+
     /**
      * Returns whether this and $other overlap in their time.
      * @param slot $other the other slot
@@ -229,6 +253,7 @@ public function prepare_for_api(): array {
             'size' => $this->size,
             'fullness' => $this->get_fullness(),
             'forcuruser' => $this->get_forcuruser(),
+            'supervisors' => $this->get_supervisors(),
         ];
     }
 
@@ -248,6 +273,9 @@ public static function api_structure(): external_single_structure {
                 'size' => new external_value(PARAM_INT, 'total capacity of the slot'),
                 'fullness' => new external_value(PARAM_INT, 'how many people have already reserved this slot'),
                 'forcuruser' => new external_value(PARAM_BOOL, 'whether the current user has reserved this slot'),
+                'supervisors' => new external_multiple_structure(
+                    new external_value(PARAM_INT, 'this slot\'s supervisors\' userIDs')
+                ),
             ]
         );
     }