diff --git a/core/modules/field/field.api.php b/core/modules/field/field.api.php
index d0d5da9..be41854 100644
--- a/core/modules/field/field.api.php
+++ b/core/modules/field/field.api.php
@@ -276,6 +276,17 @@ function hook_field_schema($field) {
 }
 
 /**
+ * Allows modules to alter the schema for a field.
+ *
+ * @param $schema
+ *   The schema definition as returned by hook_field_schema().
+ * @param $field
+ *   The field definition.
+ */
+function hook_schema_alter(&$schema, $field) {
+}
+
+/**
  * Define custom load behavior for this module's field types.
  *
  * Unlike most other field hooks, this hook operates on multiple entities. The
diff --git a/core/modules/field/field.crud.inc b/core/modules/field/field.crud.inc
index e34c0c5..bdd329e 100644
--- a/core/modules/field/field.crud.inc
+++ b/core/modules/field/field.crud.inc
@@ -129,6 +129,7 @@ function field_create_field($field) {
   module_load_install($field['module']);
   $schema = (array) module_invoke($field['module'], 'field_schema', $field);
   $schema += array('columns' => array(), 'indexes' => array(), 'foreign keys' => array());
+  drupal_alter('field_schema', $schema, $field);
   // 'columns' are hardcoded in the field type.
   $field['columns'] = $schema['columns'];
   // 'foreign keys' are hardcoded in the field type.
@@ -241,6 +242,7 @@ function field_update_field($field) {
   module_load_install($field['module']);
   $schema = (array) module_invoke($field['module'], 'field_schema', $field);
   $schema += array('columns' => array(), 'indexes' => array());
+  drupal_alter('field_schema', $schema, $field);
   // 'columns' are hardcoded in the field type.
   $field['columns'] = $schema['columns'];
   // 'indexes' can be both hardcoded in the field type, and specified in the
@@ -368,6 +370,7 @@ function field_read_fields($params = array(), $include_additional = array()) {
     module_load_install($field['module']);
     $schema = (array) module_invoke($field['module'], 'field_schema', $field);
     $schema += array('columns' => array(), 'indexes' => array());
+    drupal_alter('field_schema', $schema, $field);
     $field['columns'] = $schema['columns'];
 
     $field_name = $field['field_name'];