diff --git a/runtime/doc/starting.txt b/runtime/doc/starting.txt
index f5b33a8..ec095a4 100644
--- a/runtime/doc/starting.txt
+++ b/runtime/doc/starting.txt
@@ -346,7 +346,7 @@
 <
 --log {filename}					*--log*
 		Start logging and write entries to {filename}.
-		This works like calling `ch_logfile({filename}, 'a')` very
+		This works like calling `ch_logfile({filename}, 'ao')` very
 		early during startup.
 		{only available with the +channel feature}