diff --git a/qutebrowser/misc/mhtml.py b/qutebrowser/misc/mhtml.py
index 4eece95c4..01f8f5cc9 100644
--- a/qutebrowser/misc/mhtml.py
+++ b/qutebrowser/misc/mhtml.py
@@ -130,7 +130,7 @@ class MHTMLWriter(object):
         _files: Mapping of location->_File struct.
     """
 
-    BOUNDARY = b"---qute-mhtml-" + str(uuid4()).encode("ascii")
+    BOUNDARY = b"---=_qute-" + str(uuid4()).encode("ascii")
 
     def __init__(self, root_content=None, content_location=None,
                  content_type=None):