diff --git a/core/modules/system/tests/fixtures/update/drupal-8.entity-test-initial.php b/core/modules/system/tests/fixtures/update/drupal-8.entity-test-initial.php
new file mode 100644
index 0000000000..e7ab6961e6
--- /dev/null
+++ b/core/modules/system/tests/fixtures/update/drupal-8.entity-test-initial.php
@@ -0,0 +1,24 @@
+<?php
+// @codingStandardsIgnoreFile
+
+use Drupal\Core\Database\Database;
+
+$connection = Database::getConnection();
+
+// Simulate an entity type that had previously set an initial key schema for a
+// field.
+$schema = $connection->select('key_value')
+  ->fields('key_value', ['value'])
+  ->condition('collection', 'entity.storage_schema.sql')
+  ->condition('name', 'entity_test_update.field_schema_data.name')
+  ->execute()
+  ->fetchField();
+
+$schema = unserialize($schema);
+$schema['entity_test_update']['fields']['name']['initial'] = 'test';
+
+$connection->update('key_value')
+  ->fields(['value' => serialize($schema)])
+  ->condition('collection', 'entity.storage_schema.sql')
+  ->condition('name', 'entity_test_update.field_schema_data.name')
+  ->execute();
diff --git a/core/modules/system/tests/src/Functional/Update/EntityUpdateInitialTest.php b/core/modules/system/tests/src/Functional/Update/EntityUpdateInitialTest.php
new file mode 100644
index 0000000000..d4d79f96b5
--- /dev/null
+++ b/core/modules/system/tests/src/Functional/Update/EntityUpdateInitialTest.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace Drupal\Tests\system\Functional\Update;
+
+use Drupal\FunctionalTests\Update\UpdatePathTestBase;
+
+/**
+ * Tests handling of existing initial keys during updates.
+ *
+ * @see https://www.drupal.org/project/drupal/issues/2925550
+ *
+ * @group Update
+ */
+class EntityUpdateInitialTest extends UpdatePathTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setDatabaseDumpFiles() {
+    $this->databaseDumpFiles = [
+      __DIR__ . '/../../../fixtures/update/drupal-8.0.0-rc1-filled.standard.entity_test_update.php.gz',
+      __DIR__ . '/../../../fixtures/update/drupal-8.entity-test-initial.php',
+    ];
+  }
+
+  /**
+   * Tests that a pre-existing initial key in the field schema is not a change.
+   */
+  public function testInitialIsIgnored() {
+    $this->runUpdates();
+  }
+
+}