diff --git a/entityreference_autocomplete.module b/entityreference_autocomplete.module
index e0e687f..eabd33b 100644
--- a/entityreference_autocomplete.module
+++ b/entityreference_autocomplete.module
@@ -95,7 +95,7 @@ function entityreference_autocomplete_element_info() {
  * @return string
  *   The value to be placed in $element['#value'].
  */
-function entityreference_autocomplete_value_callback(array $element, $edit = FALSE, &$form_state) {
+function entityreference_autocomplete_value_callback(array $element, $edit = FALSE, &$form_state = array()) {
   // Just process the value when $edit comes as FALSE (no form submission), and
   // if there are default values specified, transform them into proper labels.
   if ($edit === FALSE && !empty($element['#default_value'])) {