diff --git a/core/lib/Drupal/Core/Config/TypedConfigManager.php b/core/lib/Drupal/Core/Config/TypedConfigManager.php
index 12f1849..e31eab6 100644
--- a/core/lib/Drupal/Core/Config/TypedConfigManager.php
+++ b/core/lib/Drupal/Core/Config/TypedConfigManager.php
@@ -43,6 +43,15 @@ class TypedConfigManager extends TypedDataManager implements TypedConfigManagerI
   protected $definitions;
 
   /**
+   * The array of plugin definitions that correspond to entity types.
+   *
+   * This array is keyed by entity type ID, not by plugin ID.
+   *
+   * @var array
+   */
+  protected $entityTypeDefinitions = [];
+
+  /**
    * Creates a new typed configuration manager.
    *
    * @param \Drupal\Core\Config\StorageInterface $configStorage
@@ -160,14 +169,17 @@ public function getDefinition($base_plugin_id, $exception_on_invalid = TRUE, $is
    * {@inheritdoc}
    */
   public function getDefinitionForEntityType($entity_type_id) {
-    $id = 'undefined';
-    foreach ($this->getDefinitions() as $definition_id => $definition) {
-      if (isset($definition['config_entity_type']) && $definition['config_entity_type'] === $entity_type_id) {
-        $id = $definition_id;
-        break;
+    if (!isset($this->entityTypeDefinitions[$entity_type_id])) {
+      $id = 'undefined';
+      foreach ($this->getDefinitions() as $definition_id => $definition) {
+        if (isset($definition['config_entity_type']) && $definition['config_entity_type'] === $entity_type_id) {
+          $id = $definition_id;
+          break;
+        }
       }
+      $this->entityTypeDefinitions[$entity_type_id] = $this->getDefinition($id);
     }
-    return $this->getDefinition($id);
+    return $this->entityTypeDefinitions[$entity_type_id];
   }
 
   /**
@@ -175,6 +187,7 @@ public function getDefinitionForEntityType($entity_type_id) {
    */
   public function clearCachedDefinitions() {
     $this->schemaStorage->reset();
+    $this->entityTypeDefinitions = [];
     parent::clearCachedDefinitions();
   }
 
diff --git a/core/tests/Drupal/Tests/Core/Config/TypedConfigManagerTest.php b/core/tests/Drupal/Tests/Core/Config/TypedConfigManagerTest.php
index 71a091d..9fedbf4 100644
--- a/core/tests/Drupal/Tests/Core/Config/TypedConfigManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Config/TypedConfigManagerTest.php
@@ -39,12 +39,17 @@ public function testGetDefinitionForEntityType($entity_type_id, $expected) {
       ->disableOriginalConstructor()
       ->setMethods(['getDefinitions'])
       ->getMock();
-    $manager->expects($this->any())
+    // Once for the initial loop and once from within getDefintion().
+    $manager->expects($this->exactly(2))
       ->method('getDefinitions')
       ->willReturn($definitions);
 
     $definition = $manager->getDefinitionForEntityType($entity_type_id);
     $this->assertSame($expected, $definition);
+
+    // Ensure this doesn't loop over getDefinitions() twice.
+    $definition = $manager->getDefinitionForEntityType($entity_type_id);
+    $this->assertSame($expected, $definition);
   }
 
   /**