diff --git a/ZIP.md b/ZIP.md
index a264c30..1cd596b 100644
--- a/ZIP.md
+++ b/ZIP.md
@@ -4,6 +4,8 @@ Koreader can read files stored/compressed in [ZIP files](https://en.wikipedia.or
 
 Koreader does not create zip files nor does it offer ZIP browsing support.
 
+If a filename only ends in /zip it is opened by default by the MuPDF engine. This means a ZIP of images will open in the same was as a file with a CBZ extension.
+
 ## Naming Convention
 
   * fb2.zip - FictionBook
@@ -13,5 +15,6 @@ Koreader does not create zip files nor does it offer ZIP browsing support.
   * md.zip - Markdown
   * rtf.zip - Rich Text Format
   * txt.zip - plain text
+  * .zip - opened my MuPDF, assumed to be a zip file of images
 
 If the documents are not named like this, the wrong reader/format engine is likely to be used and "No reader engine for this file of invalid file" will be displayed. Either rename the file to match conventions so that opening normally "just-works" or long-pressing the filename and then choose "Open with.." and select the correct engine. For more information see https://github.com/koreader/koreader/issues/9986