diff --git a/core/modules/block/block.install b/core/modules/block/block.install
index ee72e0f..56b91c3 100644
--- a/core/modules/block/block.install
+++ b/core/modules/block/block.install
@@ -324,6 +324,36 @@ function block_update_8003() {
 }
 
 /**
+ * Rename default menu names.
+ */
+function block_update_8004() {
+  // System menu's new block deltas are prefixed with 'menu-'.
+  $map = array(
+    'navigation' => 'menu-tools',
+    'management' => 'menu-admin',
+    'user-menu' => 'menu-account',
+    'main-menu' => 'menu-main',
+  );
+  foreach ($map as $old => $new) {
+    db_update('block')
+      ->condition('module', 'system')
+      ->condition('delta', $old)
+      ->fields(array('delta' => $new))
+      ->execute();
+    db_update('block_language')
+      ->condition('module', 'system')
+      ->condition('delta', $old)
+      ->fields(array('delta' => $new))
+      ->execute();
+    db_update('block_role')
+      ->condition('module', 'system')
+      ->condition('delta', $old)
+      ->fields(array('delta' => $new))
+      ->execute();
+  }
+}
+
+/**
  * @} End of "addtogroup updates-7.x-to-8.x".
  * The next series of updates should start at 9000.
  */
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
index 4eb7683..b09f2d4 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
@@ -322,7 +322,7 @@ function testBlock() {
     // Select the Administration menu block to be configured and moved.
     $block = array();
     $block['module'] = 'system';
-    $block['delta'] = 'admin';
+    $block['delta'] = 'menu-admin';
     $block['title'] = $this->randomName(8);
 
     // Set block title to confirm that interface works and override any custom titles.
diff --git a/core/modules/contextual/contextual.module b/core/modules/contextual/contextual.module
index df2ba1a..bbb00e8 100644
--- a/core/modules/contextual/contextual.module
+++ b/core/modules/contextual/contextual.module
@@ -128,7 +128,7 @@ function contextual_preprocess(&$variables, $hook) {
  *   menu_contextual_links(). For example:
  *   @code
  *     array('#contextual_links' => array(
- *       'block' => array('admin/structure/block/manage', array('system', 'tools')),
+ *       'block' => array('admin/structure/block/manage', array('system', 'menu-tools')),
  *       'menu' => array('admin/structure/menu/manage', array('tools')),
  *     ))
  *   @endcode
diff --git a/core/modules/node/node.install b/core/modules/node/node.install
index a9c2c36..570cb26 100644
--- a/core/modules/node/node.install
+++ b/core/modules/node/node.install
@@ -692,6 +692,26 @@ function node_update_8007() {
 }
 
 /**
+ * Rename default menu names.
+ */
+function node_update_8008() {
+  // System menu's new block deltas are prefixed with 'menu-'.
+  $map = array(
+    'navigation' => 'menu-tools',
+    'management' => 'menu-admin',
+    'user-menu' => 'menu-account',
+    'main-menu' => 'menu-main',
+  );
+  foreach ($map as $old => $new) {
+    db_update('block_node_type')
+      ->condition('module', 'system')
+      ->condition('delta', $old)
+      ->fields(array('delta' => $new))
+      ->execute();
+  }
+}
+
+/**
  * @} End of "addtogroup updates-7.x-to-8.x"
  * The next series of updates should start at 9000.
  */
diff --git a/core/modules/system/lib/Drupal/system/Tests/Menu/BreadcrumbTest.php b/core/modules/system/lib/Drupal/system/Tests/Menu/BreadcrumbTest.php
index b9df6a3..e4ecbfc 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Menu/BreadcrumbTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Menu/BreadcrumbTest.php
@@ -46,7 +46,7 @@ function setUp() {
         'status' => 1,
       ))
       ->condition('module', 'system')
-      ->condition('delta', 'tools')
+      ->condition('delta', 'menu-tools')
       ->execute();
   }
 
@@ -354,7 +354,7 @@ function testBreadCrumbs() {
       // ('taxonomy/term/%') should never be translated and appear in any menu
       // other than the breadcrumb trail.
       $elements = $this->xpath('//div[@id=:menu]/descendant::a[@href=:href]', array(
-        ':menu' => 'block-system-tools',
+        ':menu' => 'block-system-menu-tools',
         ':href' => url($link['link_path']),
       ));
       $this->assertTrue(count($elements) == 1, "Link to {$link['link_path']} appears only once.");
diff --git a/core/modules/system/lib/Drupal/system/Tests/Menu/RouterTest.php b/core/modules/system/lib/Drupal/system/Tests/Menu/RouterTest.php
index 72bcf3f..a550048 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Menu/RouterTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Menu/RouterTest.php
@@ -45,7 +45,7 @@ function setUp() {
     db_merge('block')
       ->key(array(
         'module' => 'system',
-        'delta' => 'tools',
+        'delta' => 'menu-tools',
         'theme' => 'bartik',
       ))
       ->fields(array(
diff --git a/core/modules/system/lib/Drupal/system/Tests/Menu/TrailTest.php b/core/modules/system/lib/Drupal/system/Tests/Menu/TrailTest.php
index 66c6ff8..21ae3f9 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Menu/TrailTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Menu/TrailTest.php
@@ -43,7 +43,7 @@ function setUp() {
         'status' => 1,
       ))
       ->condition('module', 'system')
-      ->condition('delta', 'tools')
+      ->condition('delta', 'menu-tools')
       ->execute();
 
     // This test puts menu links in the Administration menu and then tests for
@@ -56,7 +56,7 @@ function setUp() {
         'status' => 1,
       ))
       ->condition('module', 'system')
-      ->condition('delta', 'admin')
+      ->condition('delta', 'menu-admin')
       ->execute();
   }
 
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index a9d951b..7f9f33a 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -2515,11 +2515,13 @@ function system_block_info() {
     'status' => 1,
   );
   // System-defined menu blocks.
+  // The block deltas need to be prefixed with 'menu-', since the 'main' menu
+  // would otherwise clash with the 'main' page content block defined above.
   foreach (menu_list_system_menus() as $menu_name => $title) {
-    $blocks[$menu_name]['info'] = t($title);
+    $blocks['menu-' . $menu_name]['info'] = t($title);
     // Menu blocks can't be cached because each menu item can have
     // a custom access callback. menu.inc manages its own caching.
-    $blocks[$menu_name]['cache'] = DRUPAL_NO_CACHE;
+    $blocks['menu-' . $menu_name]['cache'] = DRUPAL_NO_CACHE;
   }
   return $blocks;
 }
@@ -2546,6 +2548,8 @@ function system_block_view($delta = '') {
       $block['content'] = menu_get_active_help();
       return $block;
     default:
+      // Strip off 'menu-' prefix from block delta.
+      $delta = substr($delta, 5);
       // All system menu blocks.
       $system_menus = menu_list_system_menus();
       if (isset($system_menus[$delta])) {
diff --git a/core/profiles/minimal/minimal.install b/core/profiles/minimal/minimal.install
index a25fdec..4e42e6d 100644
--- a/core/profiles/minimal/minimal.install
+++ b/core/profiles/minimal/minimal.install
@@ -28,7 +28,7 @@ function minimal_install() {
     ),
     array(
       'module' => 'system',
-      'delta' => 'tools',
+      'delta' => 'menu-tools',
       'theme' => $default_theme,
       'status' => 1,
       'weight' => 0,
@@ -38,7 +38,7 @@ function minimal_install() {
     ),
     array(
       'module' => 'system',
-      'delta' => 'management',
+      'delta' => 'menu-admin',
       'theme' => $default_theme,
       'status' => 1,
       'weight' => 1,
diff --git a/core/profiles/standard/standard.install b/core/profiles/standard/standard.install
index 87fb69f..b4dc761 100644
--- a/core/profiles/standard/standard.install
+++ b/core/profiles/standard/standard.install
@@ -110,7 +110,7 @@ function standard_install() {
     ),
     array(
       'module' => 'system',
-      'delta' => 'tools',
+      'delta' => 'menu-tools',
       'theme' => $default_theme,
       'status' => 1,
       'weight' => 0,