diff --git a/library/HTMLPurifier/AttrDef/CSS/Filter.php b/library/HTMLPurifier/AttrDef/CSS/Filter.php
index 31fe8bc9..7f46688c 100644
--- a/library/HTMLPurifier/AttrDef/CSS/Filter.php
+++ b/library/HTMLPurifier/AttrDef/CSS/Filter.php
@@ -19,6 +19,7 @@ class HTMLPurifier_AttrDef_CSS_Filter extends HTMLPurifier_AttrDef
     
     public function validate($value, $config, &$context) {
         $value = $this->parseCDATA($value);
+        if ($value === 'none') return $value;
         // if we looped this we could support multiple filters
         $function_length = strcspn($value, '(');
         $function = trim(substr($value, 0, $function_length));
diff --git a/tests/HTMLPurifier/AttrDef/CSS/FilterTest.php b/tests/HTMLPurifier/AttrDef/CSS/FilterTest.php
index 046d3bae..a7aa4817 100644
--- a/tests/HTMLPurifier/AttrDef/CSS/FilterTest.php
+++ b/tests/HTMLPurifier/AttrDef/CSS/FilterTest.php
@@ -10,6 +10,8 @@ class HTMLPurifier_AttrDef_CSS_FilterTest extends HTMLPurifier_AttrDefHarness
         
         $this->def = new HTMLPurifier_AttrDef_CSS_Filter();
         
+        $this->assertDef('none');
+        
         $this->assertDef('alpha(opacity=0)');
         $this->assertDef('alpha(opacity=100)');
         $this->assertDef('alpha(opacity=50)');