diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 5439b018..0bf14b76 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -18,7 +18,30 @@
 * Patches should always be submitted via a either Github "pull request" or a
   via emailed patches created using "git format-patch".
 * Patches for new features should include tests and documentation.
-* Commit messages should follow the ["How to Write a Git Commit Message"](https://chris.beams.io/posts/git-commit/) guide.
+* Commit messages should follow the ["How to Write a Git Commit Message"](https://chris.beams.io/posts/git-commit/) guide:
+  1. Separate subject from body with a blank line
+  2. Limit the subject line to 50 characters
+  3. Capitalize the subject line
+  4. Do not end the subject line with a period
+  5. Use the imperative mood in the subject line
+  6. Wrap the body at 72 characters
+  7. Use the body to explain what and why vs. how
+
+  Additional rule: the commit message may contain a prefix. The prefix must
+  contain the name of the feature or source file related to the commit and must
+  end with a colon followed by the message body.
+
+  Examples of good commit messages:
+  1. Fix typo
+  2. Update CHANGELOG.md
+  3. Add ACT file format support
+  4. ogg_vorbis: Fix granule position when seeking Vorbis streams
+
+  Examples of bad commit messages:
+  1. Fixed bug (rule 5)
+  2. update docs (rule 3)
+  3. Add very cool feature. (rule 4)
+
 * Patches to fix bugs should either pass all tests, or modify the tests in some
   sane way.
 * When a new feature is added for a particular file format and that feature