diff --git a/src/Mailer.php b/src/Mailer.php
index e8a3654..a179312 100644
--- a/src/Mailer.php
+++ b/src/Mailer.php
@@ -70,7 +70,8 @@ public function send(Submission $submission, bool $runValidation = true): bool
         if ($submission->attachment !== null) {
             $allowedFileTypes = Craft::$app->getConfig()->getGeneral()->allowedFileExtensions;
 
-            foreach ($submission->attachment as $attachment) {
+            $attachments = is_array($submission->attachment) ? $submission->attachment : [$submission->attachment];
+            foreach ($attachments as $attachment) {
                 if (!$attachment) {
                     continue;
                 }
diff --git a/src/controllers/SendController.php b/src/controllers/SendController.php
index d263d5f..bc446b4 100644
--- a/src/controllers/SendController.php
+++ b/src/controllers/SendController.php
@@ -47,7 +47,7 @@ public function actionIndex()
             if (is_array($_FILES['attachment']['name'])) {
                 $submission->attachment = UploadedFile::getInstancesByName('attachment');
             } else {
-                $submission->attachment = [UploadedFile::getInstanceByName('attachment')];
+                $submission->attachment = UploadedFile::getInstanceByName('attachment');
             }
         }