diff --git a/HACKING b/HACKING
index 46a7249616..349015499f 100644
--- a/HACKING
+++ b/HACKING
@@ -50,6 +50,10 @@ You can prevent yourself from accidentally pushing unsigned commits to Savannah
 by using the pre-push Git hook called 'pre-push'. It's located at
 'etc/git/pre-push'.
 
+When pushing a commit on behalf of somebody else, please add a Signed-off-by
+line at the end of the commit log message (e.g. with ‘git am --signoff’).
+This improves tracking of who did what.
+
 For anything else, please post to guix-patches@gnu.org and leave time for a
 review, without committing anything.  If you didn’t receive any reply
 after two weeks, and if you’re confident, it’s OK to commit.