core/includes/bootstrap.inc                        |  2 +-
 .../system/Tests/Bootstrap/PageCacheTest.php       | 25 +++++++++++++++++++---
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index a824957..e5f980e 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -816,7 +816,7 @@ function drupal_send_headers($default_headers = array(), $only_default = FALSE)
  * fresh page on every request. This prevents authenticated users from seeing
  * locally cached pages.
  *
- * Also give each page a unique ETag. This will force clients to include both
+ * Also give each page a unique ETag. This should force clients to include both
  * an If-Modified-Since header and an If-None-Match header when doing
  * conditional requests for the page (required by RFC 2616, section 13.3.4),
  * making the validation more robust. This is a workaround for a bug in Mozilla
diff --git a/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php
index fdf16b9..150e1db 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php
@@ -128,21 +128,40 @@ function testConditionalRequests() {
 
     $this->drupalGet('', array(), array('If-Modified-Since: ' . $last_modified, 'If-None-Match: ' . $etag));
     $this->assertResponse(304, 'Conditional request returned 304 Not Modified.');
+    $this->assertTrue(strlen($this->drupalGetContent()) == 0, 'No HTML returned.');
 
     $this->drupalGet('', array(), array('If-Modified-Since: ' . gmdate(DATE_RFC822, strtotime($last_modified)), 'If-None-Match: ' . $etag));
     $this->assertResponse(304, 'Conditional request with obsolete If-Modified-Since date returned 304 Not Modified.');
+    $this->assertTrue(strlen($this->drupalGetContent()) == 0, 'No HTML returned.');
 
     $this->drupalGet('', array(), array('If-Modified-Since: ' . gmdate(DATE_RFC850, strtotime($last_modified)), 'If-None-Match: ' . $etag));
     $this->assertResponse(304, 'Conditional request with obsolete If-Modified-Since date returned 304 Not Modified.');
+    $this->assertTrue(strlen($this->drupalGetContent()) == 0, 'No HTML returned.');
 
     $this->drupalGet('', array(), array('If-Modified-Since: ' . $last_modified));
+    $this->assertResponse(304, 'Conditional request with If-Modified-Since but without If-None-Match returned 304 Not Modified.');
+    $this->assertTrue(strlen($this->drupalGetContent()) == 0, 'No HTML returned.');
+
+    $this->drupalGet('', array(), array('If-None-Match: ' . $etag));
+    $this->assertResponse(304, 'Conditional request with If-None-Match but without If-Modified-Since returned 304 Not Modified.');
+    $this->assertTrue(strlen($this->drupalGetContent()) == 0, 'No HTML returned.');
+
+    $this->drupalGet('', array(), array('If-Modified-Since: ' . gmdate(DATE_RFC1123, strtotime($last_modified) + 1), 'If-None-Match: ' . $etag));
+    $this->assertResponse(200, 'Conditional request with an If-Modified-Since date newer than Last-Modified returned 200 OK.');
     // Verify the page is not printed twice when the cache is warm.
     $this->assertNoPattern('#<html.*<html#');
-    $this->assertResponse(200, 'Conditional request without If-None-Match returned 200 OK.');
     $this->assertEqual($this->drupalGetHeader('X-Drupal-Cache'), 'HIT', 'Page was cached.');
 
-    $this->drupalGet('', array(), array('If-Modified-Since: ' . gmdate(DATE_RFC1123, strtotime($last_modified) + 1), 'If-None-Match: ' . $etag));
-    $this->assertResponse(200, 'Conditional request with new a If-Modified-Since date newer than Last-Modified returned 200 OK.');
+    $this->drupalGet('', array(), array('If-Modified-Since: ' . $last_modified, 'If-None-Match: ' . $etag . '-is-invalid'));
+    $this->assertResponse(200, 'Conditional request with an invalid If-None-Match ETag value returned 200 OK.');
+    // Verify the page is not printed twice when the cache is warm.
+    $this->assertNoPattern('#<html.*<html#');
+    $this->assertEqual($this->drupalGetHeader('X-Drupal-Cache'), 'HIT', 'Page was cached.');
+
+    $this->drupalGet('', array(), array('If-Modified-Since: ' . gmdate(DATE_RFC1123, strtotime($last_modified) + 1), 'If-None-Match: ' . $etag . '-is-invalid'));
+    $this->assertResponse(200, 'Conditional request with an If-Modified-Since date nwer than Last-Modified and an invalid If-None-Match ETag value returned 200 OK.');
+    // Verify the page is not printed twice when the cache is warm.
+    $this->assertNoPattern('#<html.*<html#');
     $this->assertEqual($this->drupalGetHeader('X-Drupal-Cache'), 'HIT', 'Page was cached.');
 
     $user = $this->drupalCreateUser();