diff --git a/index.bs b/index.bs
index 83e32a8..5258ba3 100644
--- a/index.bs
+++ b/index.bs
@@ -1190,7 +1190,7 @@ which switches on |type| and runs the associated steps:
 
   * Use |mimeType| as part of the Data URL if it is available
     in keeping with the Data URL specification [[!RFC2397]].
-  * If |mimeType| is not available return a Data URL without a media-type. [[!RFC2397]].
+  * If |mimeType| is not available return a Data URL with media-type "application/octet-stream". [[!RFC2397]].
 
   Issue(104): Better specify how the DataURL is generated.