diff --git a/core/lib/Drupal/Core/Cache/ApcuBackend.php b/core/lib/Drupal/Core/Cache/ApcuBackend.php
index 7f04f0e900b330477f8cc1a067166fbb4f885413..b64fd7177bd6c410ebdc0e3eda882a229f02e90b 100644
--- a/core/lib/Drupal/Core/Cache/ApcuBackend.php
+++ b/core/lib/Drupal/Core/Cache/ApcuBackend.php
@@ -68,7 +68,7 @@ public function __construct($bin, $site_prefix, CacheTagsChecksumInterface $chec
    * @return string
    *   The APCu key for the cache item ID.
    */
-  protected function getApcuKey($cid) {
+  public function getApcuKey($cid) {
     return $this->binPrefix . $cid;
   }
 
@@ -178,14 +178,8 @@ public function set($cid, $data, $expire = CacheBackendInterface::CACHE_PERMANEN
     $cache->serialized = 0;
     $cache->data = $data;
 
-    // apc_store()'s $ttl argument can be omitted but also set to 0 (zero),
-    // in which case the value will persist until it's removed from the cache or
-    // until the next cache clear, restart, etc. This is what we want to do
-    // when $expire equals CacheBackendInterface::CACHE_PERMANENT.
-    if ($expire === CacheBackendInterface::CACHE_PERMANENT) {
-      $expire = 0;
-    }
-    apc_store($this->getApcuKey($cid), $cache, $expire);
+    // Expiration is handled by our own prepareItem(), not APCu.
+    apc_store($this->getApcuKey($cid), $cache);
   }
 
   /**
diff --git a/core/modules/system/src/Tests/Cache/ApcuBackendUnitTest.php b/core/modules/system/src/Tests/Cache/ApcuBackendUnitTest.php
index fcb55779c806c7b02563ef270a67816f97254e83..fafac7ed4ce0c877cc14d102e8ae2f8c43ca553b 100644
--- a/core/modules/system/src/Tests/Cache/ApcuBackendUnitTest.php
+++ b/core/modules/system/src/Tests/Cache/ApcuBackendUnitTest.php
@@ -87,6 +87,15 @@ public function testSetGet() {
       return;
     }
     parent::testSetGet();
+
+    // Make sure entries are permanent (i.e. no TTL).
+    $backend = $this->getCacheBackend($this->getTestBin());
+    $key = $backend->getApcuKey('TEST8');
+    foreach (new \APCIterator('user', '/^' . $key . '/') as $item) {
+      $this->assertEqual(0, $item['ttl']);
+      $found = TRUE;
+    }
+    $this->assertTrue($found);
   }
 
   /**