diff --git a/core/lib/Drupal/Component/Plugin/Discovery/DerivativeDiscoveryDecorator.php b/core/lib/Drupal/Component/Plugin/Discovery/DerivativeDiscoveryDecorator.php
index f60c8b2..208bf0e 100644
--- a/core/lib/Drupal/Component/Plugin/Discovery/DerivativeDiscoveryDecorator.php
+++ b/core/lib/Drupal/Component/Plugin/Discovery/DerivativeDiscoveryDecorator.php
@@ -50,7 +50,7 @@ public function getDefinition($plugin_id) {
         // If a plugin defined itself as a derivative, merge in possible
         // defaults from the derivative.
         if ($derivative_id && isset($plugin_definition)) {
-          $plugin_definition += $derivative_plugin_definition ?: array();
+          $plugin_definition = $this->mergeDerivativeDefinition($plugin_definition, $derivative_plugin_definition);
         }
         else {
           $plugin_definition = $derivative_plugin_definition;
@@ -90,10 +90,7 @@ protected function getDerivatives(array $base_plugin_definitions) {
           // Use this definition as defaults if a plugin already defined
           // itself as this derivative.
           if ($derivative_id && isset($base_plugin_definitions[$plugin_id])) {
-            $filtered_base = array_filter($base_plugin_definitions[$plugin_id]);
-            $derivative_definition = $filtered_base + ($derivative_definition ?: array());
-            // Add back any empty keys that the derivative didn't have.
-            $derivative_definition += $base_plugin_definitions[$plugin_id];
+            $derivative_definition = $this->mergeDerivativeDefinition($base_plugin_definitions[$plugin_id], $derivative_definition);
           }
           $plugin_definitions[$plugin_id] = $derivative_definition;
         }
@@ -203,6 +200,26 @@ protected function getDerivativeClass($base_definition) {
   }
 
   /**
+   * Merges a base and derivative definition, taking into account empty values.
+   *
+   * @param array $base_plugin_definition
+   *   The base plugin definition.
+   * @param array $derivative_definition
+   *   The derivative plugin definition.
+   *
+   * @return array
+   *   The merged definition.
+   */
+  protected function mergeDerivativeDefinition($base_plugin_definition, $derivative_definition) {
+    // Use this definition as defaults if a plugin already defined itself as
+    // this derivative, but filter out empty values first.
+    $filtered_base = array_filter($base_plugin_definition);
+    $derivative_definition = $filtered_base + ($derivative_definition ?: array());
+    // Add back any empty keys that the derivative didn't have.
+    return $derivative_definition + $base_plugin_definition;
+  }
+
+  /**
    * Passes through all unknown calls onto the decorated object.
    */
   public function __call($method, $args) {
diff --git a/core/tests/Drupal/Tests/Core/Plugin/Discovery/DerivativeDiscoveryDecoratorTest.php b/core/tests/Drupal/Tests/Core/Plugin/Discovery/DerivativeDiscoveryDecoratorTest.php
index 002f071..c22c201 100644
--- a/core/tests/Drupal/Tests/Core/Plugin/Discovery/DerivativeDiscoveryDecoratorTest.php
+++ b/core/tests/Drupal/Tests/Core/Plugin/Discovery/DerivativeDiscoveryDecoratorTest.php
@@ -159,4 +159,44 @@ public function testExistingDerivative() {
     $this->assertArrayEquals($expected, $returned_definitions['non_container_aware_discovery:test_discovery_1']);
   }
 
+  /**
+   * Tests a single definition when a derivative already exists.
+   */
+  public function testSingleExistingDerivative() {
+    $base_definition = array(
+      'id' => 'non_container_aware_discovery',
+      'derivative' => '\Drupal\Tests\Core\Plugin\Discovery\TestDerivativeDiscovery',
+      'string' => 'string',
+      'empty_string' => 'not_empty',
+      'array' => array('one', 'two'),
+      'empty_array' => array('three'),
+      'null_value' => TRUE,
+    );
+    // This will clash with a derivative id.
+    // @see \Drupal\Tests\Core\Plugin\Discovery\TestDerivativeDiscovery
+    $derivative_definition = array(
+      'id' => 'non_container_aware_discovery:test_discovery_1',
+      'string' => 'string',
+      'empty_string' => '',
+      'array' => array('one', 'two'),
+      'empty_array' => array(),
+      'null_value' => NULL,
+    );
+
+    $this->discoveryMain->expects($this->at(0))
+      ->method('getDefinition')
+      ->with('non_container_aware_discovery:test_discovery_1')
+      ->will($this->returnValue($derivative_definition));
+    $this->discoveryMain->expects($this->at(1))
+      ->method('getDefinition')
+      ->with('non_container_aware_discovery')
+      ->will($this->returnValue($base_definition));
+
+    $discovery = new DerivativeDiscoveryDecorator($this->discoveryMain);
+
+    $expected = $base_definition;
+    $expected['id'] = 'non_container_aware_discovery:test_discovery_1';
+    $this->assertArrayEquals($expected, $discovery->getDefinition('non_container_aware_discovery:test_discovery_1'));
+  }
+
 }