diff --git a/src/PhotosApi.php b/src/PhotosApi.php
index 0e472c9..916d872 100644
--- a/src/PhotosApi.php
+++ b/src/PhotosApi.php
@@ -474,7 +474,8 @@ public function getSets($photoIds, $userId = null)
             }
             foreach ($sets['photoset'] as $photoset) {
                 foreach ($photoIds as $photoId) {
-                    if (in_array($photoId, $photoset['has_requested_photos'])) {
+                    // has_requested_photos is only set if the user owns the photo.
+                    if (in_array($photoId, $photoset['has_requested_photos'] ?? [])) {
                         $out[] = $photoset;
                     }
                 }