diff --git a/S3/S3.py b/S3/S3.py
index ad0ccc9d7..8b0acd254 100644
--- a/S3/S3.py
+++ b/S3/S3.py
@@ -413,6 +413,7 @@ def object_put(self, filename, uri, extra_headers = None, extra_label = ""):
 
         ## MIME-type handling
         content_type = self.config.mime_type
+        content_encoding = None
         if filename != "-" and not content_type and self.config.guess_mime_type:
             (content_type, content_encoding) = mime_magic(filename)
         if not content_type: