diff --git a/docs/apworld specification.md b/docs/apworld specification.md
index ac89a46e..ba2f2dbb 100644
--- a/docs/apworld specification.md	
+++ b/docs/apworld specification.md	
@@ -7,10 +7,12 @@ See [world api.md](world%20api.md) for details.
 apworld provides a way to package and ship a world that is not part of the main distribution by placing a `*.apworld`
 file into the worlds folder.
 
+**Warning:** apworlds have to be all lower case, otherwise they raise a bogus Exception when trying to import in frozen python 3.10+!
+
 
 ## File Format
 
-apworld files are zip archives with the case-sensitive file ending `.apworld`.
+apworld files are zip archives, all lower case, with the file ending `.apworld`.
 The zip has to contain a folder with the same name as the zip, case-sensitive, that contains what would normally be in
 the world's folder in `worlds/`. I.e. `worlds/ror2.apworld` containing `ror2/__init__.py`.