diff --git a/src/Symfony/Component/HttpFoundation/IpUtils.php b/src/Symfony/Component/HttpFoundation/IpUtils.php
index fb906b6812..e08301ece1 100644
--- a/src/Symfony/Component/HttpFoundation/IpUtils.php
+++ b/src/Symfony/Component/HttpFoundation/IpUtils.php
@@ -57,18 +57,19 @@ class IpUtils
      * @param string $requestIp IPv4 address to check
      * @param string $ip        IPv4 address or subnet in CIDR notation
      *
-     * @return bool Whether the IP is valid
+     * @return bool Whether the request IP matches the IP, or whether the request IP is within the CIDR subnet.
      */
     public static function checkIp4($requestIp, $ip)
     {
         if (false !== strpos($ip, '/')) {
-            if ('0.0.0.0/0' === $ip) {
-                return true;
-            }
-
             list($address, $netmask) = explode('/', $ip, 2);
 
-            if ($netmask < 1 || $netmask > 32) {
+            if ($netmask === '0') {
+                // Ensure IP is valid - using ip2long below implicitly validates, but we need to do it manually here
+                return filter_var($address, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4);
+            }
+
+            if ($netmask < 0 || $netmask > 32) {
                 return false;
             }
         } else {
diff --git a/src/Symfony/Component/HttpFoundation/Tests/IpUtilsTest.php b/src/Symfony/Component/HttpFoundation/Tests/IpUtilsTest.php
index 0002478246..e87baea34a 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/IpUtilsTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/IpUtilsTest.php
@@ -30,13 +30,13 @@ class IpUtilsTest extends \PHPUnit_Framework_TestCase
             array(true, '192.168.1.1', '192.168.1.1/1'),
             array(true, '192.168.1.1', '192.168.1.0/24'),
             array(false, '192.168.1.1', '1.2.3.4/1'),
-            array(false, '192.168.1.1', '192.168.1/33'),
+            array(false, '192.168.1.1', '192.168.1.1/33'), // invalid subnet
             array(true, '192.168.1.1', array('1.2.3.4/1', '192.168.1.0/24')),
             array(true, '192.168.1.1', array('192.168.1.0/24', '1.2.3.4/1')),
             array(false, '192.168.1.1', array('1.2.3.4/1', '4.3.2.1/1')),
             array(true, '1.2.3.4', '0.0.0.0/0'),
-            array(false, '1.2.3.4', '256.256.256/0'),
-            array(false, '1.2.3.4', '192.168.1.0/0'),
+            array(true, '1.2.3.4', '192.168.1.0/0'),
+            array(false, '1.2.3.4', '256.256.256/0'), // invalid CIDR notation
         );
     }