diff --git a/lib/Doctrine/Expression.php b/lib/Doctrine/Expression.php
index 9ced16eb0..bf0d4ebb9 100644
--- a/lib/Doctrine/Expression.php
+++ b/lib/Doctrine/Expression.php
@@ -661,6 +661,15 @@ class Doctrine_Expression extends Doctrine_Connection_Module
     {
         throw new Doctrine_Expression_Exception('method not implemented');
     }
+    /**
+     * returns arcus cosine SQL string
+     *
+     * @return string
+     */
+    public function acos($value)
+    {
+        return 'ACOS(' . $value . ')';
+    }
     /**
      * __call
      *
@@ -671,5 +680,6 @@ class Doctrine_Expression extends Doctrine_Connection_Module
     	if ($this->conn->getAttribute(Doctrine::ATTR_PORTABILITY) & Doctrine::PORTABILITY_EXPR) {
             throw new Doctrine_Expression_Exception('Unknown expression ' . $m);
         }
+        return $m . '()';
     }
 }