diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index e170f27ac12fdf6b0bf5173d77ee00038d152f1e..3b3f8334277e102c1331fdf7e8845923609ea26e 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -914,7 +914,8 @@ function request_uri() {
  * Log a system message.
  *
  * @param $type
- *   The category to which this message belongs.
+ *   The category to which this message belongs. Can be any string, but the
+ *   general practice is to use the name of the module calling watchdog().
  * @param $message
  *   The message to store in the log. See t() for documentation
  *   on how $message and $variables interact. Keep $message
@@ -924,7 +925,8 @@ function request_uri() {
  *   NULL if message is already translated or not possible to
  *   translate.
  * @param $severity
- *   The severity of the message, as per RFC 3164
+ *   The severity of the message, as per RFC 3164. Possible values are
+ *   WATCHDOG_ERROR, WATCHDOG_WARNING, etc.
  * @param $link
  *   A link to associate with the message.
  *