diff --git a/TODO.md b/TODO.md
index 5433c93..807288f 100644
--- a/TODO.md
+++ b/TODO.md
@@ -27,6 +27,17 @@ Update `README.md` accordingly.
 
 # Completed Steps
 
+- 2026-08-09: replaced `hugo.toml`'s deprecated `languageCode` key with `locale`
+  (closes #18). Hugo deprecated `languageCode` in v0.158.0, so the Hugo pinned
+  in the preceding commit warns about it; left alone it would become a third
+  routinely-ignored warning, and a latent breakage when the key is removed.
+  Deliberately sequenced **after** the Hugo version move and in the same branch:
+  under the apk hugo 0.139.0 that CI ran until now, `locale` is an unknown key
+  that is silently ignored, which downgrades the generated RSS from
+  `<language>en-us</language>` to `<language>en</language>` with no warning and
+  exit 0. Verified on hugo v0.164.0 that the RSS `<language>` still reads
+  `en-us`, the `lang` attribute is unchanged, and `public/` is byte-identical to
+  the preceding commit's output
 - 2026-08-09: installed Hugo at a deliberate, hash-verified version instead of
   taking whatever alpine ships (closes #26). `script/bootstrap` no longer does
   `pkg_install hugo`; it installs `github.com/gohugoio/hugo@v0.164.0` with
diff --git a/hugo.toml b/hugo.toml
index a58301b..5a43c1b 100644
--- a/hugo.toml
+++ b/hugo.toml
@@ -1,5 +1,5 @@
 baseURL = 'https://lora.vegas/'
-languageCode = 'en-us'
+locale = 'en-us'
 title = 'LoRa Vegas — Las Vegas Meshtastic Community'
 theme = 'loravega'