diff --git a/lib/ContextStackTrait.php b/lib/ContextStackTrait.php
index d1b756f..ee3a3ba 100644
--- a/lib/ContextStackTrait.php
+++ b/lib/ContextStackTrait.php
@@ -57,6 +57,26 @@ trait ContextStackTrait {
      */
     public $namespaceMap = [];
 
+    /**
+     * This is a list of custom serializers for specific classes.
+     *
+     * The writer may use this if you attempt to serialize an object with a
+     * class that does not implement XmlSerializable.
+     *
+     * Instead it will look at this classmap to see if there is a custom
+     * serializer here. This is useful if you don't want your value objects
+     * to be responsible for serializing themselves.
+     *
+     * The keys in this classmap need to be fully qualified PHP class names,
+     * the values must be callbacks. The callbacks take two arguments. The
+     * writer class, and the value that must be written.
+     *
+     * function (Writer $writer, object $value)
+     *
+     * @var array
+     */
+    public $classMap = [];
+
     /**
      * Backups of previous contexts.
      *
@@ -78,7 +98,8 @@ function pushContext() {
         $this->contextStack[] = [
             $this->elementMap,
             $this->contextUri,
-            $this->namespaceMap
+            $this->namespaceMap,
+            $this->classMap
         ];
 
     }
@@ -93,7 +114,8 @@ function popContext() {
         list(
             $this->elementMap,
             $this->contextUri,
-            $this->namespaceMap
+            $this->namespaceMap,
+            $this->classMap
         ) = array_pop($this->contextStack);
 
     }
diff --git a/lib/Service.php b/lib/Service.php
index 2aa1c9a..8625a00 100644
--- a/lib/Service.php
+++ b/lib/Service.php
@@ -38,6 +38,26 @@ class Service {
      */
     public $namespaceMap = [];
 
+    /**
+     * This is a list of custom serializers for specific classes.
+     *
+     * The writer may use this if you attempt to serialize an object with a
+     * class that does not implement XmlSerializable.
+     *
+     * Instead it will look at this classmap to see if there is a custom
+     * serializer here. This is useful if you don't want your value objects
+     * to be responsible for serializing themselves.
+     *
+     * The keys in this classmap need to be fully qualified PHP class names,
+     * the values must be callbacks. The callbacks take two arguments. The
+     * writer class, and the value that must be written.
+     *
+     * function (Writer $writer, object $value)
+     *
+     * @var array
+     */
+    public $classMap = [];
+
     /**
      * Returns a fresh XML Reader
      *
@@ -60,6 +80,7 @@ function getWriter() {
 
         $w = new Writer();
         $w->namespaceMap = $this->namespaceMap;
+        $w->classMap = $this->classMap;
         return $w;
 
     }
diff --git a/lib/Writer.php b/lib/Writer.php
index 4edba33..d417479 100644
--- a/lib/Writer.php
+++ b/lib/Writer.php
@@ -100,8 +100,14 @@ function write($value) {
 
         if (is_scalar($value)) {
             $this->text($value);
-        } elseif ($value instanceof XmlSerializable) {
+        } elseif (is_object($value) && $value instanceof XmlSerializable) {
+
             $value->xmlSerialize($this);
+
+        } elseif (is_object($value) && isset($this->classMap[get_class($value)])) {
+            $this->classMap[get_class($value)]($this, $value);
+        } elseif (is_callable($value)) {
+            $value($this);
         } elseif (is_null($value)) {
             // noop
         } elseif (is_array($value)) {
@@ -142,7 +148,11 @@ function write($value) {
 
         } elseif (is_object($value)) {
 
-            throw new InvalidArgumentException('The writer cannot serialize objects of type: ' . get_class($value));
+            throw new InvalidArgumentException('The writer cannot serialize objects of class: ' . get_class($value));
+
+        } else {
+
+            throw new InvalidArgumentException('The writer cannot serialize values of type: ' . gettype($value));
 
         }
 
diff --git a/tests/Sabre/Xml/WriterTest.php b/tests/Sabre/Xml/WriterTest.php
index c48da51..44f581f 100644
--- a/tests/Sabre/Xml/WriterTest.php
+++ b/tests/Sabre/Xml/WriterTest.php
@@ -323,6 +323,49 @@ function testStartElementSimple() {
 
         $this->assertEquals($output, $this->writer->outputMemory());
 
+    }
+
+    function testCallback() {
+
+        $this->compare([
+            '{http://sabredav.org/ns}root' => function(Writer $writer) {
+                $writer->text('deferred writer');
+            },
+        ], <<<HI
+<?xml version="1.0"?>
+<s:root xmlns:s="http://sabredav.org/ns">deferred writer</s:root>
+
+HI
+        );
+
+    }
+
+    function testClassMap() {
+
+        $obj = (object)[
+            'key1' => 'value1',
+            'key2' => 'value2',
+        ];
+
+        $this->writer->classMap['stdClass'] = function(Writer $writer, $value) {
+
+            foreach (get_object_vars($value) as $key => $val) {
+                $writer->writeElement('{http://sabredav.org/ns}' . $key, $val);
+            }
+
+        };
+
+        $this->compare([
+            '{http://sabredav.org/ns}root' => $obj
+        ], <<<HI
+<?xml version="1.0"?>
+<s:root xmlns:s="http://sabredav.org/ns">
+ <s:key1>value1</s:key1>
+ <s:key2>value2</s:key2>
+</s:root>
+
+HI
+        );
 
     }
 }