Index: masquerade.module
===================================================================
--- masquerade.module	(revision 2375)
+++ masquerade.module	(working copy)
@@ -34,6 +34,10 @@
 function masquerade_init() {
   global $user;
 
+  if (empty($user->uid)) {
+    return;
+  }
+
   // load from table uid + session id
   $uid = db_result(db_query("SELECT uid_from FROM {masquerade} WHERE sid = '%s' AND uid_as = %d", session_id(), $user->uid));
   // using if so that we get unset rather than false if not masqing
@@ -540,7 +544,7 @@
 function masquerade_switch_user($uid) {
   global $user;
 
-  if (!is_numeric($uid)) {
+  if (!is_numeric($uid) || empty($uid)) {
     drupal_set_message(t('A user id was not correctly passed to the switching function.'));
     watchdog('masquerade', 'The user id provided to switch users was not numeric.', NULL, WATCHDOG_ERROR);
     return drupal_goto(referer_uri());