diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index efddf00..6d9379f 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -1261,7 +1261,7 @@ function drupal_page_header() {
 
   $default_headers = array(
     'Expires' => 'Sun, 19 Nov 1978 05:00:00 GMT',
-    'Cache-Control' => 'no-cache, must-revalidate, post-check=0, pre-check=0',
+    'Cache-Control' => 'no-cache, no-store, must-revalidate, post-check=0, pre-check=0',
   );
   drupal_send_headers($default_headers);
 }
diff --git a/modules/image/image.test b/modules/image/image.test
index 3591979..5937fb2 100644
--- a/modules/image/image.test
+++ b/modules/image/image.test
@@ -251,7 +251,7 @@ class ImageStylesPathAndUrlTestCase extends DrupalWebTestCase {
     $this->assertEqual($this->drupalGetHeader('Content-Length'), $generated_image_info['file_size'], 'Expected Content-Length was reported.');
     if ($scheme == 'private') {
       $this->assertEqual($this->drupalGetHeader('Expires'), 'Sun, 19 Nov 1978 05:00:00 GMT', 'Expires header was sent.');
-      $this->assertEqual($this->drupalGetHeader('Cache-Control'), 'no-cache, must-revalidate, post-check=0, pre-check=0', 'Cache-Control header was set to prevent caching.');
+      $this->assertEqual($this->drupalGetHeader('Cache-Control'), 'no-cache, no-core, must-revalidate, post-check=0, pre-check=0', 'Cache-Control header was set to prevent caching.');
       $this->assertEqual($this->drupalGetHeader('X-Image-Owned-By'), 'image_module_test', 'Expected custom header has been added.');
 
       // Make sure that a second request to the already existing derivate works
diff --git a/modules/simpletest/tests/bootstrap.test b/modules/simpletest/tests/bootstrap.test
index ece1cd9..14dd632 100644
--- a/modules/simpletest/tests/bootstrap.test
+++ b/modules/simpletest/tests/bootstrap.test
@@ -191,7 +191,7 @@ class BootstrapPageCacheTestCase extends DrupalWebTestCase {
     $this->drupalGet('system-test/set-header', array('query' => array('name' => 'Foo', 'value' => 'bar')));
     $this->assertFalse($this->drupalGetHeader('X-Drupal-Cache'), 'Caching was bypassed.');
     $this->assertTrue(strpos($this->drupalGetHeader('Vary'), 'Cookie') === FALSE, 'Vary: Cookie header was not sent.');
-    $this->assertEqual($this->drupalGetHeader('Cache-Control'), 'no-cache, must-revalidate, post-check=0, pre-check=0', 'Cache-Control header was sent.');
+    $this->assertEqual($this->drupalGetHeader('Cache-Control'), 'no-cache, no-core, must-revalidate, post-check=0, pre-check=0', 'Cache-Control header was sent.');
     $this->assertEqual($this->drupalGetHeader('Expires'), 'Sun, 19 Nov 1978 05:00:00 GMT', 'Expires header was sent.');
     $this->assertEqual($this->drupalGetHeader('Foo'), 'bar', 'Custom header was sent.');