diff --git a/.github/workflows/deploy-site.yml b/.github/workflows/deploy-site.yml
index d998e8f..b8c59de 100644
--- a/.github/workflows/deploy-site.yml
+++ b/.github/workflows/deploy-site.yml
@@ -44,3 +44,6 @@ jobs:
           publish_branch: gh-pages
           publish_dir: site/dist
           force_orphan: true
+          # Keep the custom-domain CNAME file on gh-pages; without this,
+          # force_orphan would delete it on every deploy and detach the domain.
+          cname: progit3.com
diff --git a/site/README.md b/site/README.md
index f709e14..82c715b 100644
--- a/site/README.md
+++ b/site/README.md
@@ -62,8 +62,8 @@ The file name (without `.mdx`) becomes the URL: `/blog/<file-name>/`.
 publishes `site/dist/` to the `gh-pages` branch with
 [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages).
 Point GitHub Pages at the `gh-pages` branch (Settings → Pages → Deploy from a
-branch) and the site is served at <https://progit.github.io/progit3/>.
+branch) and the site is served at <https://progit3.com/>.
 
-The canonical URL and base path default to `https://progit.github.io` and
-`/progit3`; override them with the `SITE_URL` and `BASE_PATH` environment
-variables (e.g. for a fork or a custom domain).
+The canonical URL and base path default to `https://progit3.com` and
+`/`; override them with the `SITE_URL` and `BASE_PATH` environment
+variables (e.g. for a fork served at `https://<user>.github.io/progit3/`).
diff --git a/site/astro.config.mjs b/site/astro.config.mjs
index c2a51c3..406804c 100644
--- a/site/astro.config.mjs
+++ b/site/astro.config.mjs
@@ -2,10 +2,10 @@
 import { defineConfig } from 'astro/config';
 import mdx from '@astrojs/mdx';
 
-// GitHub Pages project site: https://progit.github.io/progit3/
-// Override SITE_URL / BASE_PATH for forks or a custom domain.
-const site = process.env.SITE_URL ?? 'https://progit.github.io';
-const base = process.env.BASE_PATH ?? '/progit3';
+// GitHub Pages with a custom domain: https://progit3.com/
+// Override SITE_URL / BASE_PATH for forks (e.g. https://<user>.github.io and /progit3).
+const site = process.env.SITE_URL ?? 'https://progit3.com';
+const base = process.env.BASE_PATH ?? '/';
 
 export default defineConfig({
   site,
diff --git a/site/scripts/build-book.mjs b/site/scripts/build-book.mjs
index 41ff942..f27b4cd 100644
--- a/site/scripts/build-book.mjs
+++ b/site/scripts/build-book.mjs
@@ -22,7 +22,7 @@ import { fileURLToPath } from 'node:url';
 
 const siteRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
 const repoRoot = path.resolve(siteRoot, '..');
-const base = (process.env.BASE_PATH ?? '/progit3').replace(/\/+$/, '');
+const base = (process.env.BASE_PATH ?? '/').replace(/\/+$/, '');
 
 // ---------------------------------------------------------------------------
 // 1. Make sure book/contributors.txt exists (mirrors the Rakefile task).