diff --git a/modules/field/field.api.php b/modules/field/field.api.php
index 9b3ebf0f5441930f97b3e7df8b92f1093c590193..415e8935c6aa1be3274cc038caf7ce1c92e24402 100644
--- a/modules/field/field.api.php
+++ b/modules/field/field.api.php
@@ -2178,6 +2178,71 @@ function hook_field_extra_fields_display_alter(&$displays, $context) {
     $displays['description']['visibility'] = FALSE;
   }
 }
+
+/**
+ * Alters the widget properties of a field instance before it gets displayed.
+ *
+ * Note that instead of hook_field_widget_properties_alter(), which is called
+ * for all fields on all entity types,
+ * hook_field_widget_properties_ENTITY_TYPE_alter() may be used to alter widget
+ * properties for fields on a specific entity type only.
+ *
+ * This hook is called once per field per added or edit entity. If the result
+ * of the hook involves reading from the database, it is highly recommended to
+ * statically cache the information.
+ *
+ * @param $widget
+ *   The instance's widget properties.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The entity type; e.g. 'node' or 'user'.
+ *   - entity: The entity object.
+ *   - field: The field that the widget belongs to.
+ *   - instance: The instance of the field.
+ *
+ * @see hook_field_widget_properties_ENTITY_TYPE_alter()
+ */
+function hook_field_widget_properties_alter(&$widget, $context) {
+  // Change a widget's type according to the time of day.
+  $field = $context['field'];
+  if ($context['entity_type'] == 'node' && $field['field_name'] == 'field_foo') {
+    $time = date('H');
+    $widget['type'] = $time < 12 ? 'widget_am' : 'widget_pm';
+  }
+}
+
+/**
+ * Alters the widget properties of a field instance on a given entity type
+ * before it gets displayed.
+ *
+ * Modules can implement hook_field_widget_properties_ENTITY_TYPE_alter() to
+ * alter the widget properties for fields on a specific entity type, rather than
+ * implementing hook_field_widget_properties_alter().
+ *
+ * This hook is called once per field per displayed widget entity. If the result
+ * of the hook involves reading from the database, it is highly recommended to
+ * statically cache the information.
+ *
+ * @param $widget
+ *   The instance's widget properties.
+ * @param $context
+ *   An associative array containing:
+ *   - entity_type: The entity type; e.g. 'node' or 'user'.
+ *   - entity: The entity object.
+     - field: The field that the widget belongs to.
+ *   - instance: The instance of the field.
+ *
+ * @see hook_field_widget_properties_alter()
+ */
+function hook_field_widget_properties_ENTITY_TYPE_alter(&$widget, $context) {
+  // Change a widget's type according to the time of day.
+  $field = $context['field'];
+  if ($field['field_name'] == 'field_foo') {
+    $time = date('H');
+    $widget['type'] = $time < 12 ? 'widget_am' : 'widget_pm';
+  }
+}
+
 /**
  * @} End of "ingroup field_storage"
  */
diff --git a/modules/field/field.form.inc b/modules/field/field.form.inc
index d5778dfc56843d61976bf6b07f980c9100f105d1..474cc7f5b752d9d18fa2b72964ed99787f113737 100644
--- a/modules/field/field.form.inc
+++ b/modules/field/field.form.inc
@@ -25,6 +25,15 @@ function field_default_form($entity_type, $entity, $field, $instance, $langcode,
     $items = field_get_default_value($entity_type, $entity, $field, $instance, $langcode);
   }
 
+  // Let modules alter the widget properties.
+  $context = array(
+    'entity_type' => $entity_type,
+    'entity' => $entity,
+    'field' => $field,
+    'instance' => $instance,
+  );
+  drupal_alter(array('field_widget_properties', 'field_widget_properties_' . $entity_type), $instance['widget'], $context);
+
   // Collect widget elements.
   $elements = array();
   if (field_access('edit', $field, $entity_type, $entity)) {