diff --git a/src/Attachment.php b/src/Attachment.php
index 38190fa..71eef6b 100644
--- a/src/Attachment.php
+++ b/src/Attachment.php
@@ -81,6 +81,10 @@ public function save(string $path): false|int
      */
     public function extension(): ?string
     {
+        if (! $this->filename) {
+            return null;
+        }
+
         if ($ext = pathinfo($this->filename, PATHINFO_EXTENSION)) {
             return $ext;
         }