diff -u b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
--- b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
+++ b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
@@ -761,7 +761,13 @@
   public function __clone() {
     // Ensure the itemDefinition property is actually cloned
     // by overwriting the original reference.
-    $this->itemDefinition = FieldItemDataDefinition::create($this);
+    $this->itemDefinition = clone $this->itemDefinition;
+
+    // The itemDefinition (\Drupal\Core\Field\TypedData\FieldItemDataDefinition)
+    // has a property fieldDefinition, which is a recursive reference to the
+    // parent BaseFieldDefinition. Need to overwrite the reference to the old
+    // object with a reference to the cloned one.
+    $this->itemDefinition->setFieldDefinition($this);
   }
 
 }