diff --git a/NEWS b/NEWS
index 199b8cc8..feadcb10 100644
--- a/NEWS
+++ b/NEWS
@@ -17,6 +17,7 @@ NEWS ( CHANGELOG and HISTORY )                                     HTMLPurifier
   (mostly harmless, except for the fact that it would be a little slower)
 - Configuration objects with different serials do not clobber each
   others when revision numbers are unequal
+- Improve Serializer DefinitionCache directory permissions checks
 . Rewire some test-cases to swallow errors rather than expect them
 . HTMLDefinition printer updated with some of the new attributes
 . DefinitionCache keys reordered to reflect precedence: version number,
diff --git a/library/HTMLPurifier/DefinitionCache/Serializer.php b/library/HTMLPurifier/DefinitionCache/Serializer.php
index 8272a5af..a03b584d 100644
--- a/library/HTMLPurifier/DefinitionCache/Serializer.php
+++ b/library/HTMLPurifier/DefinitionCache/Serializer.php
@@ -21,14 +21,14 @@ class HTMLPurifier_DefinitionCache_Serializer extends
         if (!$this->checkDefType($def)) return;
         $file = $this->generateFilePath($config);
         if (file_exists($file)) return false;
-        $this->_prepareDir($config);
+        if (!$this->_prepareDir($config)) return false;
         return $this->_write($file, serialize($def));
     }
     
     function set($def, $config) {
         if (!$this->checkDefType($def)) return;
         $file = $this->generateFilePath($config);
-        $this->_prepareDir($config);
+        if (!$this->_prepareDir($config)) return false;
         return $this->_write($file, serialize($def));
     }
     
@@ -36,7 +36,7 @@ class HTMLPurifier_DefinitionCache_Serializer extends
         if (!$this->checkDefType($def)) return;
         $file = $this->generateFilePath($config);
         if (!file_exists($file)) return false;
-        $this->_prepareDir($config);
+        if (!$this->_prepareDir($config)) return false;
         return $this->_write($file, serialize($def));
     }
     
@@ -53,6 +53,7 @@ class HTMLPurifier_DefinitionCache_Serializer extends
     }
     
     function flush($config) {
+        if (!$this->_prepareDir($config)) return false;
         $dir = $this->generateDirectoryPath($config);
         $dh  = opendir($dir);
         while (false !== ($filename = readdir($dh))) {
@@ -63,7 +64,7 @@ class HTMLPurifier_DefinitionCache_Serializer extends
     }
     
     function cleanup($config) {
-        $this->_prepareDir($config);
+        if (!$this->_prepareDir($config)) return false;
         $dir = $this->generateDirectoryPath($config);
         $dh  = opendir($dir);
         while (false !== ($filename = readdir($dh))) {
@@ -125,12 +126,64 @@ class HTMLPurifier_DefinitionCache_Serializer extends
     
     /**
      * Prepares the directory that this type stores the serials in
+     * @return True if successful
      */
     function _prepareDir($config) {
         $directory = $this->generateDirectoryPath($config);
         if (!is_dir($directory)) {
+            $base = $this->generateBaseDirectoryPath($config);
+            if (!is_dir($base)) {
+                trigger_error('Base directory '.$base.' does not exist,
+                    please create or change using %Cache.SerializerPath',
+                    E_USER_ERROR);
+                return false;
+            } elseif (!$this->_testPermissions($base)) {
+                return false;
+            }
             mkdir($directory);
+        } elseif (!$this->_testPermissions($directory)) {
+            return false;
         }
+        return true;
+    }
+    
+    /**
+     * Tests permissions on a directory and throws out friendly
+     * error messages and attempts to chmod it itself if possible
+     */
+    function _testPermissions($dir) {
+        // early abort, if it is writable, everything is hunky-dory
+        if (is_writable($dir)) return true;
+        if (!is_dir($dir)) {
+            // generally, you'll want to handle this beforehand
+            // so a more specific error message can be given
+            trigger_error('Directory '.$dir.' does not exist',
+                E_USER_ERROR);
+            return false;
+        }
+        if (function_exists('posix_getuid')) {
+            // POSIX system, we can give more specific advice
+            if (fileowner($dir) === posix_getuid()) {
+                // we can chmod it ourselves
+                chmod($dir, 0755);
+                return true;
+            } elseif (filegroup($dir) === posix_getgid()) {
+                $chmod = '775';
+            } else {
+                // PHP's probably running as nobody, so we'll
+                // need to give global permissions
+                $chmod = '777';
+            }
+            trigger_error('Directory '.$dir.' not writable, '.
+                'please chmod to ' . $chmod,
+                E_USER_ERROR);
+        } else {
+            // generic error message
+            trigger_error('Directory '.$dir.' not writable, '.
+                'please alter file permissions',
+                E_USER_ERROR);
+        }
+        return false;
     }
     
 }