diff --git a/docs/markdown/backend/overview.md b/docs/markdown/backend/overview.md
index 0c2092a..ca7de86 100644
--- a/docs/markdown/backend/overview.md
+++ b/docs/markdown/backend/overview.md
@@ -1,6 +1,7 @@
 # 💽 Backends
 
 Backends are the outputs of the backup process. Each location needs at least one.
+Note: names of backends MUST be lower case!
 
 ```yaml | .autorestic.yml
 version: 2