diff --git a/README.md b/README.md
index 3381e7e..6413f87 100644
--- a/README.md
+++ b/README.md
@@ -499,6 +499,8 @@ PRIVATE_KEY a path to a private SSH key used to decrypt file
 
 EDITOR environment variable of editor to use when editing FILE
 
+If STDIN is not interactive, EDITOR will be set to "cp /dev/stdin"
+
 RULES environment variable with path to Nix file specifying recipient public keys.
 Defaults to './secrets.nix'
 ```