diff --git a/CHANGELOG.md b/CHANGELOG.md
index 753bbbd..5f8ba1c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,7 +6,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 Entries for unreleased work are not written here directly. Each issue drops a
-fragment in [`changelog.d/`](changelog.d/README.md); the fragments are assembled
+fragment in [`changelog.d/`](https://github.com/riddler/statifier-ui/blob/v0.10.1/changelog.d/README.md); the fragments are assembled
 into a version section at release. See that README for the format and for when a
 change warrants an entry at all.
 
diff --git a/README.md b/README.md
index 700baf6..baa99a2 100644
--- a/README.md
+++ b/README.md
@@ -159,7 +159,7 @@ The vocabulary that stream can carry is closed and published:
 string the format defines. It is the handle to hold and diff across upgrades -
 a consumer still ignores types it does not know, but a diff of that list is
 how it notices a new one. See the note on pinning the vocabulary in
-[ADR-0005](docs/adr/0005-language-neutral-trace-wire-format.md).
+[ADR-0005](https://github.com/riddler/statifier-ui/blob/v0.10.1/docs/adr/0005-language-neutral-trace-wire-format.md).
 
 ## Checking expressions
 
diff --git a/mix.exs b/mix.exs
index c781d9f..baf4ff5 100644
--- a/mix.exs
+++ b/mix.exs
@@ -36,9 +36,9 @@ defmodule StatifierUI.MixProject do
   defp elixirc_paths(_env), do: ["lib"]
 
   # Hexdocs configuration. These paths are read off the publisher's disk at
-  # `mix docs` time and need no entry in package()'s files: list - the docs
-  # tarball hexdocs hosts is built separately from the package tarball
-  # `mix deps.get` fetches.
+  # `mix docs` time - the docs tarball hexdocs hosts is built separately from
+  # the package tarball `mix deps.get` fetches. A guide the README links to
+  # relatively is also in package()'s files: list, for hex.pm's README page.
   defp docs do
     [
       name: "StatifierUI",
@@ -69,8 +69,24 @@ defmodule StatifierUI.MixProject do
       # `assets` is here because ADR-0009 makes it public API: the JavaScript
       # ships as source and the host's bundler compiles it, so a tarball without
       # it is a package whose documented hook cannot be imported.
-      # `test/packaging_test.exs` holds this list against the ADRs.
-      files: ~w(lib assets mix.exs README.md LICENSE CHANGELOG.md),
+      # The docs/ guides are here because hex.pm renders the README from this
+      # tarball, so a README relative link answers 404 there unless its target
+      # ships; each is also an extra, so the same link works on HexDocs.
+      # `test/packaging_test.exs` holds this list against the ADRs and the
+      # README's relative links.
+      files: ~w(
+        lib
+        assets
+        mix.exs
+        README.md
+        LICENSE
+        CHANGELOG.md
+        docs/architecture.md
+        docs/ops-embedding.md
+        docs/fixture-bundles.md
+        docs/wire-format.md
+        docs/telemetry.md
+      ),
       links: %{
         "GitHub" => @source_url,
         "Changelog" => "#{@source_url}/blob/main/CHANGELOG.md"
diff --git a/test/packaging_test.exs b/test/packaging_test.exs
index 79cb44a..169a700 100644
--- a/test/packaging_test.exs
+++ b/test/packaging_test.exs
@@ -55,4 +55,41 @@ defmodule StatifierUI.PackagingTest do
       assert {"assets", "ADR-0009 (JavaScript ships as source)"} in @published_by_adr
     end
   end
+
+  describe "README relative links" do
+    # hex.pm renders the README from the package tarball, so a relative link
+    # there resolves inside the tarball and answers 404 unless the target
+    # ships; HexDocs rewrites a relative link only when the target is an
+    # extra. One relative link works on GitHub, HexDocs and hex.pm alike only
+    # when its target is in both lists. A file that is in neither (an ADR,
+    # for one) is linked by absolute GitHub URL instead.
+    test "every relative link target is in package files: and in extras" do
+      config = Mix.Project.config()
+      files = config[:package][:files]
+      extras = Enum.map(config[:docs][:extras], &extra_path/1)
+
+      targets = readme_relative_targets()
+      assert targets != [], "found no relative links in README.md; the scan is broken"
+
+      for target <- targets do
+        assert target in extras,
+               "README.md links #{target} relatively, but it is not in docs() extras: #{inspect(extras)}"
+
+        assert Enum.any?(files, &(target == &1 or String.starts_with?(target, &1 <> "/"))),
+               "README.md links #{target} relatively, but package() files: does not ship it: #{inspect(files)}"
+      end
+    end
+  end
+
+  defp readme_relative_targets do
+    ~r/\]\(([^)\s]+)\)/
+    |> Regex.scan(File.read!("README.md"), capture: :all_but_first)
+    |> List.flatten()
+    |> Enum.reject(&String.match?(&1, ~r{^(https?:|mailto:|#)}))
+    |> Enum.map(&(&1 |> String.split("#") |> hd()))
+    |> Enum.uniq()
+  end
+
+  defp extra_path({path, _opts}), do: to_string(path)
+  defp extra_path(path), do: to_string(path)
 end