diff --git a/doc/sample_hooks/post-init-add-origin b/doc/sample_hooks/post-init-add-origin
index a3030d5fa524301b4f8a2272d7719aee32e2d161..993f3c705aa9517db8d3b0d9d29e6a47a8a20af9 100755
--- a/doc/sample_hooks/post-init-add-origin
+++ b/doc/sample_hooks/post-init-add-origin
@@ -1,6 +1,18 @@
 #!/bin/sh
 
-# This adds a remote origin at $GITURL/dotfiles/$VCSH_DIRECTORY
-# Assumes $GITURL is set to the base of your remote repos.
+# This adds a remote origin at $GITURL/dotfiles/$VCSH_DIRECTORY which
+# is helpful for creating new dotfile repositories that you plan to
+# store on (e.g.) Github.
+#
+# You must set $GITURL in order to use this hook. For example, add the
+# following to your .bashrc (or equivalent for your shell), replacing
+# YOURUSERNAME with your github username:
+#
+# export GITURL="git@github.com:YOURUSERNAME"
+
+if [ -z $GITURL ]; then
+    echo "\$GITURL is not set; please see post-init-add-origin hook"
+    exit 1;
+fi
 
 vcsh $VCSH_DIRECTORY remote add origin $GITURL/dotfiles/$VCSH_DIRECTORY