diff --git a/modules/field/field.api.php b/modules/field/field.api.php
index fccf479..807ef54 100644
--- a/modules/field/field.api.php
+++ b/modules/field/field.api.php
@@ -272,6 +272,17 @@ 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 $field
+ *   The field definition.
+ */
+function hook_field_schema_alter(&$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/modules/field/field.crud.inc b/modules/field/field.crud.inc
index e34c0c5..5c0f09c 100644
--- a/modules/field/field.crud.inc
+++ b/modules/field/field.crud.inc
@@ -18,6 +18,23 @@
  */
 
 /**
+ * Retrieves the schema for a field.
+ *
+ * @param $field
+ *   The field array to get the schema definition against.
+ * @return
+ *   The field schema definition array.
+ */
+function field_retrieve_schema($field) {
+  module_load_install($field['module']);
+  $schema = (array) module_invoke($field['module'], 'field_schema', $field);
+  $schema += array('columns' => array(), 'indexes' => array(), 'foreign keys' => array());
+  // Give other modules a chance to alter this definition.
+  drupal_alter('field_schema', $schema, $field);
+  return $schema;
+}
+
+/**
  * Creates a field.
  *
  * This function does not bind the field to any bundle; use
@@ -126,9 +143,7 @@ function field_create_field($field) {
   $field['storage']['module'] = $storage_type['module'];
   $field['storage']['active'] = 1;
   // Collect storage information.
-  module_load_install($field['module']);
-  $schema = (array) module_invoke($field['module'], 'field_schema', $field);
-  $schema += array('columns' => array(), 'indexes' => array(), 'foreign keys' => array());
+  $schema = field_retrieve_schema($field);
   // 'columns' are hardcoded in the field type.
   $field['columns'] = $schema['columns'];
   // 'foreign keys' are hardcoded in the field type.
@@ -238,9 +253,7 @@ function field_update_field($field) {
 
   // Collect the new storage information, since what is in
   // $prior_field may no longer be right.
-  module_load_install($field['module']);
-  $schema = (array) module_invoke($field['module'], 'field_schema', $field);
-  $schema += array('columns' => array(), 'indexes' => array());
+  $schema = field_retrieve_schema($field);
   // 'columns' are hardcoded in the field type.
   $field['columns'] = $schema['columns'];
   // 'indexes' can be both hardcoded in the field type, and specified in the
@@ -365,9 +378,7 @@ function field_read_fields($params = array(), $include_additional = array()) {
     module_invoke_all('field_read_field', $field);
 
     // Populate storage information.
-    module_load_install($field['module']);
-    $schema = (array) module_invoke($field['module'], 'field_schema', $field);
-    $schema += array('columns' => array(), 'indexes' => array());
+    $schema = field_retrieve_schema($field);
     $field['columns'] = $schema['columns'];
 
     $field_name = $field['field_name'];