diff --git a/modules/field/field.crud.inc b/modules/field/field.crud.inc
index e4486d0..3c2128b 100644
--- a/modules/field/field.crud.inc
+++ b/modules/field/field.crud.inc
@@ -31,9 +31,7 @@
  *   Other properties, if omitted, will be given the following default values:
  *   - cardinality: 1
  *   - locked: FALSE
- *   - indexes: the field-type indexes, specified by the field type's
- *     hook_field_schema(). The indexes specified in $field are added
- *     to those default indexes. It is possible to override the
+ *   - custom indexes: An array of indexes that should override the
  *     definition of a field-type index by providing an index with the
  *     same name, or to remove it by redefining it as an empty array
  *     of columns. Overriding field-type indexes should be done
@@ -102,6 +100,7 @@ function field_create_field($field) {
     'settings' => array(),
     'storage' => array(),
     'deleted' => 0,
+    'custom indexes' => array(),
   );
 
   // Check that the field type is known.
@@ -137,12 +136,8 @@ function field_create_field($field) {
   $field['columns'] = $schema['columns'];
   // 'foreign keys' are hardcoded in the field type.
   $field['foreign keys'] = $schema['foreign keys'];
-  // 'indexes' can be both hardcoded in the field type, and specified in the
-  // incoming $field definition.
-  $field += array(
-    'indexes' => array(),
-  );
-  $field['indexes'] += $schema['indexes'];
+  // 'indexes' can be overridden by the 'custom indexes' value if set.
+  $field['indexes'] = $field['custom indexes'] + $schema['indexes'];
 
   // The serialized 'data' column contains everything from $field that does not
   // have its own column and is not automatically populated when the field is
@@ -249,12 +244,8 @@ function field_update_field($field) {
   $field['columns'] = $schema['columns'];
   // 'foreign keys' are hardcoded in the field type.
   $field['foreign keys'] = $schema['foreign keys'];
-  // 'indexes' can be both hardcoded in the field type, and specified in the
-  // incoming $field definition.
-  $field += array(
-    'indexes' => array(),
-  );
-  $field['indexes'] += $schema['indexes'];
+  // 'indexes' can be overridden by the 'custom indexes' value if set.
+  $field['indexes'] = $field['custom indexes'] + $schema['indexes'];
 
   $has_data = field_has_data($field);
 
diff --git a/modules/field/tests/field.test b/modules/field/tests/field.test
index 1e59315..5c68976 100644
--- a/modules/field/tests/field.test
+++ b/modules/field/tests/field.test
@@ -2497,7 +2497,7 @@ class FieldCrudTestCase extends FieldTestCase {
     $field_definition = array(
       'field_name' => 'field_2',
       'type' => 'test_field',
-      'indexes' => array(
+      'custom indexes' => array(
         'value' => array(),
       ),
     );
@@ -2511,7 +2511,7 @@ class FieldCrudTestCase extends FieldTestCase {
     $field_definition = array(
       'field_name' => 'field_3',
       'type' => 'test_field',
-      'indexes' => array(
+      'custom indexes' => array(
         'value_2' => array('value'),
       ),
     );
@@ -2522,6 +2522,59 @@ class FieldCrudTestCase extends FieldTestCase {
   }
 
   /**
+   * Test changing a field's schema using field_update_field().
+   */
+  function testFieldSchemaUpdate() {
+    $schema = Database::getConnection()->schema();
+
+    // Create a test field.
+    $field_definition = array(
+      'field_name' => 'test',
+      'type' => 'test_field',
+    );
+    field_create_field($field_definition);
+
+    $this->assertTrue($schema->tableExists('field_data_test'));
+    $this->assertTrue($schema->fieldExists('field_data_test', 'test_value'));
+    $this->assertTrue($schema->indexExists('field_data_test', 'test_value'));
+    $this->assertFalse($schema->fieldExists('field_data_test', 'test_value2'));
+    $this->assertFalse($schema->indexExists('field_data_test', 'test_value2'));
+
+    // Register an additional column and index for field_test_field_schema().
+    variable_set('field_test_field_schema_override', array(
+      'columns' => array(
+        'value2' => array(
+          'type' => 'int',
+          'size' => 'medium',
+          'not null' => FALSE,
+        ),
+      ),
+      'indexes' => array(
+        'value2' => array('value2'),
+      ),
+    ));
+
+    // Update the field, which should add the new value2 column and index.
+    field_update_field($field_definition);
+    $this->assertTrue($schema->tableExists('field_data_test'));
+    $this->assertTrue($schema->fieldExists('field_data_test', 'test_value'));
+    $this->assertTrue($schema->indexExists('field_data_test', 'test_value'));
+    $this->assertTrue($schema->fieldExists('field_data_test', 'test_value2'));
+    $this->assertTrue($schema->indexExists('field_data_test', 'test_value2'));
+
+    // Unregister the additional value2 column and index.
+    variable_del('field_test_field_schema_override');
+
+    // Update the field, which should now remove the value2 column and index.
+    field_update_field($field_definition);
+    $this->assertTrue($schema->tableExists('field_data_test'));
+    $this->assertTrue($schema->fieldExists('field_data_test', 'test_value'));
+    $this->assertTrue($schema->indexExists('field_data_test', 'test_value'));
+    $this->assertFalse($schema->fieldExists('field_data_test', 'test_value2'));
+    $this->assertFalse($schema->indexExists('field_data_test', 'test_value2'));
+  }
+
+  /**
    * Test the deletion of a field.
    */
   function testDeleteField() {
diff --git a/modules/field/tests/field_test.install b/modules/field/tests/field_test.install
index eaf1390..a1c6ecb 100644
--- a/modules/field/tests/field_test.install
+++ b/modules/field/tests/field_test.install
@@ -118,7 +118,7 @@ function field_test_schema() {
  */
 function field_test_field_schema($field) {
   if ($field['type'] == 'test_field') {
-    return array(
+    $schema = array(
       'columns' => array(
         'value' => array(
           'type' => 'int',
@@ -130,6 +130,10 @@ function field_test_field_schema($field) {
         'value' => array('value'),
       ),
     );
+    if ($override = variable_get('field_test_field_schema_override', array())) {
+      $schema = drupal_array_merge_deep($override, $schema);
+    }
+    return $schema;
   }
   else {
     $foreign_keys = array();