diff --git a/core/lib/Drupal/Component/ClassLoader/ApcClassLoader.php b/core/lib/Drupal/Component/ClassLoader/ApcClassLoader.php
index 7664ee5a07..56a62b88be 100644
--- a/core/lib/Drupal/Component/ClassLoader/ApcClassLoader.php
+++ b/core/lib/Drupal/Component/ClassLoader/ApcClassLoader.php
@@ -26,14 +26,14 @@ class ApcClassLoader {
    *
    * @var string[]
    */
-  protected $data = [];
+  protected $classmap = [];
 
   /**
    * A flag to whether the data should be written to disc.
    *
    * @var bool
    */
-  protected $writeData = FALSE;
+  protected $writeClassMap = FALSE;
 
   /**
    * Constructor.
@@ -98,33 +98,40 @@ public function loadClass($class) {
    * @return string|null
    */
   public function findFile($class) {
-    if (!empty($this->data[$class])) {
-      return $this->data[$class];
+    if (!empty($this->classmap[$class])) {
+      return $this->classmap[$class];
     }
-    elseif (!isset($this->data) && $data = apcu_fetch($this->prefix)) {
-      $this->data = $data;
+    elseif (!isset($this->classmap) && $data = apcu_fetch($this->prefix)) {
+      $this->classmap = $data;
     }
     else {
-      $this->data[$class] = $this->decorated->findFile($class);
-      $this->writeData = TRUE;
+      $this->classmap[$class] = $this->decorated->findFile($class);
+      $this->writeClassMap = TRUE;
     }
 
-    return $this->data[$class];
+    return $this->classmap[$class];
   }
 
   /**
    * Passes through all unknown calls onto the decorated object.
    */
   public function __call($method, $args) {
-    return call_user_func_array(array($this->decorated, $method), $args);
+    return call_user_func_array([$this->decorated, $method], $args);
   }
 
   /**
    * {@inheritdoc}
    */
   public function __destruct() {
-    if ($this->writeData) {
-      apcu_store($this->prefix, $this->data);
+    if ($this->writeClassMap) {
+      // A different request might have loaded different classes, so let's merge
+      // the data to improve efficiency.
+      if ($previous_classmap = apcu_fetch($this->prefix)) {
+        $class_map = array_merge($this->classmap, $previous_classmap);
+        if ($class_map != $previous_classmap) {
+          apcu_store($this->prefix, $this->classmap);
+        }
+      }
     }
   }