diff --git a/islandora.api.php b/islandora.api.php
index 3f00bf57..e553a894 100644
--- a/islandora.api.php
+++ b/islandora.api.php
@@ -746,7 +746,7 @@ function hook_cmodel_pid_islandora_derivative() {
 /**
  * Allows for the altering of defined derivative functions.
  */
-function hook_islandora_derivative_alter(&$derivatives, AbstractObject $object, $ds_modified_params = array()) {
+function hook_islandora_derivative_alter(&$derivatives, AbstractObject $object = NULL, $ds_modified_params = array()) {
   foreach ($derivatives as $key => $derivative) {
     if ($derivative['destination_dsid'] == 'TN') {
       unset($derivatives[$key]);
diff --git a/tests/islandora_derivatives_test.module b/tests/islandora_derivatives_test.module
index 4a46eb66..91ef8fef 100644
--- a/tests/islandora_derivatives_test.module
+++ b/tests/islandora_derivatives_test.module
@@ -48,7 +48,7 @@ function islandora_derivatives_test_some_cmodel_islandora_derivative() {
 /**
  * Implements hook_islandora_CMODEL_PID_derivative_alter().
  */
-function islandora_derivatives_test_some_cmodel_islandora_derivative_alter(&$derivatives, AbstractObject $object, $ds_modified_params) {
+function islandora_derivatives_test_some_cmodel_islandora_derivative_alter(&$derivatives, AbstractObject $object = NULL, $ds_modified_params = array()) {
   // Use a mask to determine if only the label has been modified.
   $diff = array_diff_key($ds_modified_params, array(
     'label' => NULL,