diff --git a/src/JsonSchema/Constraints/Factory.php b/src/JsonSchema/Constraints/Factory.php
index a4570f61..8cd25c1f 100644
--- a/src/JsonSchema/Constraints/Factory.php
+++ b/src/JsonSchema/Constraints/Factory.php
@@ -19,10 +19,27 @@
 class Factory
 {
     /**
-     * @var UriRetriever
+     * @var UriRetriever $uriRetriever
      */
     protected $uriRetriever;
 
+    /**
+     * @var array $constraintMap
+     */
+    protected $constraintMap = array(
+        'array' => 'JsonSchema\Constraints\CollectionConstraint',
+        'collection' => 'JsonSchema\Constraints\CollectionConstraint',
+        'object' => 'JsonSchema\Constraints\ObjectConstraint',
+        'type' => 'JsonSchema\Constraints\TypeConstraint',
+        'undefined' => 'JsonSchema\Constraints\UndefinedConstraint',
+        'string' => 'JsonSchema\Constraints\StringConstraint',
+        'number' => 'JsonSchema\Constraints\NumberConstraint',
+        'enum' => 'JsonSchema\Constraints\EnumConstraint',
+        'format' => 'JsonSchema\Constraints\FormatConstraint',
+        'schema' => 'JsonSchema\Constraints\SchemaConstraint',
+        'validator' => 'JsonSchema\Validator',
+    );
+
     /**
      * @param UriRetriever $uriRetriever
      */
@@ -43,6 +60,25 @@ public function getUriRetriever()
         return $this->uriRetriever;
     }
 
+    /**
+     * @param string $name
+     * @param string $class
+     * @return Factory
+     */
+    public function setConstraintClass($name, $class)
+    {
+      // Ensure class exists
+      if (!class_exists($class)) {
+        throw new InvalidArgumentException('Unknown constraint ' . $name);
+      }
+      // Ensure class is appropriate
+      if (!in_array('JsonSchema\Constraints\ConstraintInterface', class_implements($class))) {
+        throw new InvalidArgumentException('Invalid class ' . $name);
+      }
+      $this->constraintMap[$name] = $class;
+      return $this;
+    }
+
     /**
      * Create a constraint instance for the given constraint name.
      *
@@ -52,30 +88,9 @@ public function getUriRetriever()
      */
     public function createInstanceFor($constraintName)
     {
-        switch ($constraintName) {
-            case 'array':
-            case 'collection':
-                return new CollectionConstraint(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
-            case 'object':
-                return new ObjectConstraint(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
-            case 'type':
-                return new TypeConstraint(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
-            case 'undefined':
-                return new UndefinedConstraint(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
-            case 'string':
-                return new StringConstraint(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
-            case 'number':
-                return new NumberConstraint(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
-            case 'enum':
-                return new EnumConstraint(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
-            case 'format':
-                return new FormatConstraint(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
-            case 'schema':
-                return new SchemaConstraint(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
-            case 'validator':
-                return new Validator(Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
+        if (array_key_exists($constraintName, $this->constraintMap)) {
+          return new $this->constraintMap[$constraintName](Constraint::CHECK_MODE_NORMAL, $this->uriRetriever, $this);
         }
-
         throw new InvalidArgumentException('Unknown constraint ' . $constraintName);
     }
 }
diff --git a/tests/JsonSchema/Tests/Constraints/FactoryTest.php b/tests/JsonSchema/Tests/Constraints/FactoryTest.php
index b7c6cbe5..e3a2acab 100644
--- a/tests/JsonSchema/Tests/Constraints/FactoryTest.php
+++ b/tests/JsonSchema/Tests/Constraints/FactoryTest.php
@@ -9,9 +9,25 @@
 
 namespace JsonSchema\Tests\Constraints;
 
+use JsonSchema\Constraints\Constraint;
 use JsonSchema\Constraints\Factory;
 use PHPUnit_Framework_TestCase as TestCase;
 
+
+/**
+ * Class MyBadConstraint
+ * @package JsonSchema\Tests\Constraints
+ */
+class MyBadConstraint {}
+
+/**
+ * Class MyStringConstraint
+ * @package JsonSchema\Tests\Constraints
+ */
+class MyStringConstraint extends Constraint {
+  public function check($value, $schema = null, $path = null, $i = null){}
+}
+
 class FactoryTest extends TestCase
 {
     /**
@@ -69,10 +85,34 @@ public function testExceptionWhenCreateInstanceForInvalidConstraintName($constra
         $this->factory->createInstanceFor($constraintName);
     }
 
-    public function invalidConstraintNameProvider()
+    public function invalidConstraintNameProvider() {
+      return array(
+        array('invalidConstraintName'),
+      );
+    }
+
+    /**
+     * @expectedException InvalidArgumentException
+     */
+    public function testSetConstraintClassExistsCondition()
+    {
+      $this->factory->setConstraintClass('string', 'SomeConstraint');
+    }
+
+    /**
+     * @expectedException InvalidArgumentException
+     */
+    public function testSetConstraintClassImplementsCondition()
+    {
+      $this->factory->setConstraintClass('string', 'JsonSchema\Tests\Constraints\MyBadConstraint');
+    }
+
+    public function testSetConstraintClassInstance()
     {
-        return array(
-            array('invalidConstraintName'),
-        );
+      $this->factory->setConstraintClass('string', 'JsonSchema\Tests\Constraints\MyStringConstraint');
+      $constraint = $this->factory->createInstanceFor('string');
+      $this->assertInstanceOf('JsonSchema\Tests\Constraints\MyStringConstraint', $constraint);
+      $this->assertInstanceOf('JsonSchema\Constraints\ConstraintInterface', $constraint);
+      $this->assertSame($this->factory->getUriRetriever(), $constraint->getUriRetriever());
     }
 }