Index: modules/user/user.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.module,v
retrieving revision 1.1088
diff -u -p -r1.1088 user.module
--- modules/user/user.module	4 Dec 2009 16:49:48 -0000	1.1088
+++ modules/user/user.module	4 Dec 2009 17:51:14 -0000
@@ -2714,6 +2714,10 @@ function user_multiple_cancel_confirm_su
 
   if ($form_state['values']['confirm']) {
     foreach ($form_state['values']['accounts'] as $uid => $value) {
+      // Prevent user 1 from being deleted.
+      if ($uid <= 1) {
+        continue;
+      }
       // Prevent user administrators from deleting themselves without confirmation.
       if ($uid == $user->uid) {
         $admin_form_state = $form_state;
Index: modules/user/user.pages.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.pages.inc,v
retrieving revision 1.62
diff -u -p -r1.62 user.pages.inc
--- modules/user/user.pages.inc	1 Dec 2009 16:03:35 -0000	1.62
+++ modules/user/user.pages.inc	4 Dec 2009 18:35:38 -0000
@@ -244,7 +244,7 @@ function user_profile_form($form, &$form
       '#value' => t('Cancel account'),
       '#weight' => 31,
       '#submit' => array('user_edit_cancel_submit'),
-      '#access' => ($account->uid == $user->uid && user_access('cancel account')) || user_access('administer users'),
+      '#access' => $account->uid > 1 && (($account->uid == $user->uid && user_access('cancel account')) || user_access('administer users')),
     );
   }
 
Index: modules/user/user.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.test,v
retrieving revision 1.70
diff -u -p -r1.70 user.test
--- modules/user/user.test	1 Dec 2009 22:30:31 -0000	1.70
+++ modules/user/user.test	4 Dec 2009 18:06:44 -0000
@@ -338,6 +338,44 @@ class UserCancelTestCase extends DrupalW
   }
 
   /**
+   * Tests that user account for uid 1 cannot be cancelled.
+   *
+   * This should never be possible, or the site owner would become unable to
+   * administer the site.
+   */
+  function testUserCancelUid1() {
+    // Update uid 1's name and password to we know it.
+    $password = user_password();
+    require_once DRUPAL_ROOT . '/' . variable_get('password_inc', 'includes/password.inc');
+    $account = array(
+      'name' => 'user1',
+      'pass' => user_hash_password(trim($password)),
+    );
+    // We cannot use user_save() here or the password would be hashed again.
+    db_update('users')
+      ->fields($account)
+      ->condition('uid', 1)
+      ->execute();
+
+    // Reload and log in uid 1.
+    $user1 = user_load(1, TRUE);
+    $user1->pass_raw = $password;
+
+    // Try to cancel uid 1's account with a different user.
+    $this->admin_user = $this->drupalCreateUser(array('administer users'));
+    $this->drupalLogin($this->admin_user);
+    $edit = array(
+      'operation' => 'cancel',
+      'accounts[1]' => TRUE,
+    );
+    $this->drupalPost('admin/people', $edit, t('Update'));
+
+    // Verify that uid 1's account was not cancelled.
+    $user1 = user_load(1, TRUE);
+    $this->assertEqual($user1->status, 1, t('User #1 still exists and is not blocked.'));
+  }
+
+  /**
    * Attempt invalid account cancellations.
    */
   function testUserCancelInvalid() {
@@ -613,6 +651,8 @@ class UserCancelTestCase extends DrupalW
       $edit['accounts[' . $uid . ']'] = TRUE;
     }
     $edit['accounts[' . $admin_user->uid . ']'] = TRUE;
+    // Also try to cancel uid 1.
+    $edit['accounts[1]'] = TRUE;
     $this->drupalPost('admin/people', $edit, t('Update'));
     $this->assertText(t('Are you sure you want to cancel these user accounts?'), t('Confirmation form to cancel accounts displayed.'));
     $this->assertText(t('When cancelling these accounts'), t('Allows to select account cancellation method.'));
@@ -632,6 +672,10 @@ class UserCancelTestCase extends DrupalW
     $this->assertText(t('A confirmation request to cancel your account has been sent to your e-mail address.'), t('Account cancellation request mailed message displayed.'));
     $admin_user = user_load($admin_user->uid);
     $this->assertTrue($admin_user->status == 1, t('Administrative user is found in the database and enabled.'));
+
+    // Verify that uid 1's account was not cancelled.
+    $user1 = user_load(1, TRUE);
+    $this->assertEqual($user1->status, 1, t('User #1 still exists and is not blocked.'));
   }
 }