diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 0383856fe..924244569 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -25,7 +25,10 @@ the most useful contribution.
 From a clone, the file goes to `bios/Manufacturer/Console/filename`, and
 `python scripts/validate_pr.py path/to/file` names that folder for a file still
 outside `bios/`. Given a folder, such as an old card's BIOS folder, it checks
-every file under it. A file over the browser's 25 MB limit goes in that way.
+every file under it. A file over the browser's 25 MB limit goes in that way,
+up to the 100 MB GitHub accepts in a push. A larger file stays out of the pull
+request: [open an issue](https://github.com/Abdess/retrobios/issues/new?template=missing-bios.yml) with the hashes
+`validate_pr.py` prints, and a maintainer adds it to the `large-files` release.
 
 ## Add a platform
 
diff --git a/scripts/generate_readme.py b/scripts/generate_readme.py
index 596f62d68..01e3ac47d 100644
--- a/scripts/generate_readme.py
+++ b/scripts/generate_readme.py
@@ -37,6 +37,7 @@ from common import (
 from nativemode import check_label
 import release_record
 from siteguides import install_command
+from validate_pr import LARGE_FILE_ISSUE_URL
 from verify import verify_platform
 
 
@@ -930,7 +931,10 @@ the most useful contribution.
 From a clone, the file goes to `bios/Manufacturer/Console/filename`, and
 `python scripts/validate_pr.py path/to/file` names that folder for a file still
 outside `bios/`. Given a folder, such as an old card's BIOS folder, it checks
-every file under it. A file over the browser's 25 MB limit goes in that way.
+every file under it. A file over the browser's 25 MB limit goes in that way,
+up to the 100 MB GitHub accepts in a push. A larger file stays out of the pull
+request: [open an issue]({LARGE_FILE_ISSUE_URL}) with the hashes
+`validate_pr.py` prints, and a maintainer adds it to the `large-files` release.
 
 ## Add a platform
 
diff --git a/tests/test_contributing_text.py b/tests/test_contributing_text.py
index bf00749aa..66ced6b53 100644
--- a/tests/test_contributing_text.py
+++ b/tests/test_contributing_text.py
@@ -97,6 +97,17 @@ class BeforeOpeningAPullRequest(unittest.TestCase):
             with self.subTest(package=package):
                 self.assertRegex(pip_line, rf"\b{package}\b")
 
+    def test_a_file_too_large_for_git_has_a_route(self):
+        """The guide sent any file over 25 MB through a clone, which GitHub
+        refuses past 100 MB, and only a maintainer can write to the release."""
+        import validate_pr
+
+        text = generate_readme.generate_contributing()
+        section = text.split("## What happens next", 1)[1].split("\n## ", 1)[0]
+        self.assertEqual(validate_pr.MAX_FILE_SIZE, 100 * 1024 * 1024)
+        self.assertIn("100 MB", section)
+        self.assertIn(f"]({validate_pr.LARGE_FILE_ISSUE_URL})", section)
+
     def test_it_installs_what_the_checks_need_and_no_site_package(self):
         """The site is built by Node from website/package-lock.json: a pip
         line naming the old theme installed packages nothing reads."""