diff --git a/docs/en/cookbook/dql-user-defined-functions.rst b/docs/en/cookbook/dql-user-defined-functions.rst
index 77d66ad82..a3a7606ad 100644
--- a/docs/en/cookbook/dql-user-defined-functions.rst
+++ b/docs/en/cookbook/dql-user-defined-functions.rst
@@ -53,6 +53,17 @@ DQL query. ``$class`` is a string of a class-name which has to
 extend ``Doctrine\ORM\Query\Node\FunctionNode``. This is a class
 that offers all the necessary API and methods to implement a UDF.
 
+Instead of providing the function class name, you can also provide
+a callable that returns the function object:
+
+.. code-block:: php
+
+    <?php
+    $config = new \Doctrine\ORM\Configuration();
+    $config->addCustomStringFunction($name, function () {
+        return new MyCustomFunction();
+    });
+
 In this post we will implement some MySql specific Date calculation
 methods, which are quite handy in my opinion:
 
diff --git a/lib/Doctrine/ORM/Configuration.php b/lib/Doctrine/ORM/Configuration.php
index d9ff96b47..02433b93c 100644
--- a/lib/Doctrine/ORM/Configuration.php
+++ b/lib/Doctrine/ORM/Configuration.php
@@ -401,8 +401,8 @@ class Configuration extends \Doctrine\DBAL\Configuration
      *
      * DQL function names are case-insensitive.
      *
-     * @param string $name
-     * @param string $className
+     * @param string          $name      Function name.
+     * @param string|callable $className Class name or a callable that returns the function.
      *
      * @return void
      *
@@ -459,8 +459,8 @@ class Configuration extends \Doctrine\DBAL\Configuration
      *
      * DQL function names are case-insensitive.
      *
-     * @param string $name
-     * @param string $className
+     * @param string          $name      Function name.
+     * @param string|callable $className Class name or a callable that returns the function.
      *
      * @return void
      *
@@ -517,8 +517,8 @@ class Configuration extends \Doctrine\DBAL\Configuration
      *
      * DQL function names are case-insensitive.
      *
-     * @param string $name
-     * @param string $className
+     * @param string          $name      Function name.
+     * @param string|callable $className Class name or a callable that returns the function.
      *
      * @return void
      *
diff --git a/lib/Doctrine/ORM/Query/Parser.php b/lib/Doctrine/ORM/Query/Parser.php
index 762cf67ce..c64e731c6 100644
--- a/lib/Doctrine/ORM/Query/Parser.php
+++ b/lib/Doctrine/ORM/Query/Parser.php
@@ -3411,7 +3411,7 @@ class Parser
 
         $function = is_string($functionClass)
             ? new $functionClass($functionName)
-            : $functionClass($functionName);
+            : call_user_func($functionClass, $functionName);
 
         $function->parse($this);
 
@@ -3450,7 +3450,7 @@ class Parser
 
         $function = is_string($functionClass)
             ? new $functionClass($functionName)
-            : $functionClass($functionName);
+            : call_user_func($functionClass, $functionName);
 
         $function->parse($this);
 
@@ -3490,7 +3490,7 @@ class Parser
 
         $function = is_string($functionClass)
             ? new $functionClass($functionName)
-            : $functionClass($functionName);
+            : call_user_func($functionClass, $functionName);
 
         $function->parse($this);