diff --git a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/field_type/DateTimeItem.php b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/field_type/DateTimeItem.php
index 6f02eda9bac..558ca474426 100644
--- a/core/modules/datetime/lib/Drupal/datetime/Plugin/field/field_type/DateTimeItem.php
+++ b/core/modules/datetime/lib/Drupal/datetime/Plugin/field/field_type/DateTimeItem.php
@@ -76,7 +76,7 @@ class DateTimeItem extends ConfigFieldItemBase implements PrepareCacheInterface
   /**
    * {@inheritdoc}
    */
-  public function settingsForm(array $form, array &$form_state) {
+  public function settingsForm(array $form, array &$form_state, $has_data) {
     $element = array();
 
     $element['datetime_type'] = array(
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigEntityReferenceItemBase.php b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigEntityReferenceItemBase.php
index 80b69b69c12..92443245d41 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigEntityReferenceItemBase.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigEntityReferenceItemBase.php
@@ -125,11 +125,11 @@ class ConfigEntityReferenceItemBase extends EntityReferenceItem implements Confi
    * Copied from \Drupal\field\Plugin\field\field_type\LegacyConfigFieldItem,
    * since we cannot extend it.
    */
-  public function settingsForm(array $form, array &$form_state) {
+  public function settingsForm(array $form, array &$form_state, $has_data) {
     if ($callback = $this->getLegacyCallback('settings_form')) {
       // hook_field_settings_form() used to receive the $instance (not actually
       // needed), and the value of field_has_data().
-      return $callback($this->getInstance()->getField(), $this->getInstance(), $this->getInstance()->getField()->hasData());
+      return $callback($this->getInstance()->getField(), $this->getInstance(), $has_data);
     }
     return array();
   }
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemBase.php b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemBase.php
index 743ad5c7145..388ccbe0c08 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemBase.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemBase.php
@@ -34,7 +34,7 @@ abstract class ConfigFieldItemBase extends FieldItemBase implements ConfigFieldI
   /**
    * {@inheritdoc}
    */
-  public function settingsForm(array $form, array &$form_state) {
+  public function settingsForm(array $form, array &$form_state, $has_data) {
     return array();
   }
 
diff --git a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemInterface.php b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemInterface.php
index f37afa0dbe6..a584640d9c3 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemInterface.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemInterface.php
@@ -60,18 +60,25 @@ interface ConfigFieldItemInterface extends FieldItemInterface {
    * Returns a form for the field-level settings.
    *
    * Invoked from \Drupal\field_ui\Form\FieldEditForm to allow administrators to
-   * configure field-level settings. If the field already has data, the form
-   * should only include the settings that are safe to change.
+   * configure field-level settings.
+   *
+   * Field storage might reject field definition changes that affect the field
+   * storage schema if the field already has data. When the $has_data parameter
+   * is TRUE, the form should not allow changing the settings that take part in
+   * the schema() method. It is recommended to set #access to FALSE on the
+   * corresponding elements.
    *
    * @param array $form
    *   The form where the settings form is being included in.
    * @param array $form_state
    *   The form state of the (entire) configuration form.
+   * @param bool $has_data
+   *   TRUE if the field already has data, FALSE if not.
    *
    * @return
    *   The form definition for the field settings.
    */
-  public function settingsForm(array $form, array &$form_state);
+  public function settingsForm(array $form, array &$form_state, $has_data);
 
   /**
    * Returns a form for the instance-level settings.
diff --git a/core/modules/field/lib/Drupal/field/Plugin/field/field_type/LegacyConfigFieldItem.php b/core/modules/field/lib/Drupal/field/Plugin/field/field_type/LegacyConfigFieldItem.php
index 0bad0d0dfd4..26e0a105b68 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/field/field_type/LegacyConfigFieldItem.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/field/field_type/LegacyConfigFieldItem.php
@@ -55,11 +55,11 @@ abstract class LegacyConfigFieldItem extends ConfigFieldItemBase implements Prep
   /**
    * {@inheritdoc}
    */
-  public function settingsForm(array $form, array &$form_state) {
+  public function settingsForm(array $form, array &$form_state, $has_data) {
     if ($callback = $this->getLegacyCallback('settings_form')) {
       // hook_field_settings_form() used to receive the $instance (not actually
       // needed), and the value of field_has_data().
-      return $callback($this->getInstance()->getField(), $this->getInstance(), $this->getInstance()->getField()->hasData());
+      return $callback($this->getInstance()->getField(), $this->getInstance(), $has_data);
     }
     return array();
   }
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php b/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php
index 305596fe08b..f40e32a33b9 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php
@@ -138,7 +138,7 @@ class FieldEditForm implements FormInterface, ControllerInterface {
     // FieldItem.
     $ids = (object) array('entity_type' => $this->instance['entity_type'], 'bundle' => $this->instance['bundle'], 'entity_id' => NULL);
     $entity = _field_create_entity_from_ids($ids);
-    $form['field']['settings'] += $this->getFieldItem($entity, $field['field_name'])->settingsForm($form, $form_state);
+    $form['field']['settings'] += $this->getFieldItem($entity, $field['field_name'])->settingsForm($form, $form_state, $field->hasData());
 
     $form['actions'] = array('#type' => 'actions');
     $form['actions']['submit'] = array('#type' => 'submit', '#value' => t('Save field settings'));
diff --git a/core/modules/number/lib/Drupal/number/Plugin/field/field_type/DecimalItem.php b/core/modules/number/lib/Drupal/number/Plugin/field/field_type/DecimalItem.php
index d7ca60f55f3..927189983da 100644
--- a/core/modules/number/lib/Drupal/number/Plugin/field/field_type/DecimalItem.php
+++ b/core/modules/number/lib/Drupal/number/Plugin/field/field_type/DecimalItem.php
@@ -67,10 +67,9 @@ class DecimalItem extends NumberItemBase {
   /**
    * {@inheritdoc}
    */
-  public function settingsForm(array $form, array &$form_state) {
+  public function settingsForm(array $form, array &$form_state, $has_data) {
     $element = array();
     $settings = $this->getFieldSettings();
-    $has_data = $this->getInstance()->getField()->hasData();
 
     $element['precision'] = array(
       '#type' => 'select',
diff --git a/core/modules/text/lib/Drupal/text/Plugin/field/field_type/TextItem.php b/core/modules/text/lib/Drupal/text/Plugin/field/field_type/TextItem.php
index d048caf5653..644a2a96894 100644
--- a/core/modules/text/lib/Drupal/text/Plugin/field/field_type/TextItem.php
+++ b/core/modules/text/lib/Drupal/text/Plugin/field/field_type/TextItem.php
@@ -83,7 +83,7 @@ class TextItem extends TextItemBase {
   /**
    * {@inheritdoc}
    */
-  public function settingsForm(array $form, array &$form_state) {
+  public function settingsForm(array $form, array &$form_state, $has_data) {
     $element = array();
 
     $element['max_length'] = array(
@@ -93,9 +93,7 @@ class TextItem extends TextItemBase {
       '#required' => TRUE,
       '#description' => t('The maximum length of the field in characters.'),
       '#min' => 1,
-      // @todo: If $has_data, add a validate handler that only allows
-      // max_length to increase.
-      '#disabled' => $this->getInstance()->getField()->hasData(),
+      '#disabled' => $has_data,
     );
 
     return $element;