diff --git a/flaskfdx/upload.py b/flaskfdx/upload.py
index 1ae6db9..de06640 100644
--- a/flaskfdx/upload.py
+++ b/flaskfdx/upload.py
@@ -4,7 +4,7 @@ from flaskfdx.db import get_db
 from flaskfdx.tools import fdxsql
 
 def validate_xls_file(file):
-    if inspect_format(file) == 'xls':
+    if inspect_format(None, file.read()) == 'xls':
         return True
     else:
         return False