diff --git a/src/Rules/AllowedFile.php b/src/Rules/AllowedFile.php
index 7446c5e6f2..8f361ad783 100644
--- a/src/Rules/AllowedFile.php
+++ b/src/Rules/AllowedFile.php
@@ -120,8 +120,12 @@ public function validate(string $attribute, mixed $value, Closure $fail): void
         }
     }
 
-    private function isAllowedExtension(UploadedFile $file): bool
+    private function isAllowedExtension(mixed $file): bool
     {
+        if (! $file instanceof UploadedFile) {
+            return false;
+        }
+
         $extensions = $this->allowedExtensions ?? array_merge(static::EXTENSIONS, config('statamic.assets.additional_uploadable_extensions', []));
 
         return in_array(trim(strtolower($file->getClientOriginalExtension())), $extensions);