diff --git a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
index 426d6e8a5743..ac6a56095a27 100644
--- a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
@@ -52,7 +52,7 @@ function ($key, $value, $isHit) use ($defaultLifetime) {
             null,
             CacheItem::class
         );
-        $getId = function ($key) { return $this->getId((string) $key); };
+        $getId = \Closure::fromCallable(array($this, 'getId'));
         $this->mergeByLifetime = \Closure::bind(
             function ($deferred, $namespace, &$expiredIds) use ($getId) {
                 $byLifetime = array();
@@ -60,6 +60,7 @@ function ($deferred, $namespace, &$expiredIds) use ($getId) {
                 $expiredIds = array();
 
                 foreach ($deferred as $key => $item) {
+                    $key = (string) $key;
                     if (null === $item->expiry) {
                         $byLifetime[0 < $item->defaultLifetime ? $item->defaultLifetime : 0][$getId($key)] = $item->value;
                     } elseif ($item->expiry > $now) {
diff --git a/src/Symfony/Component/Cache/Adapter/TagAwareAdapter.php b/src/Symfony/Component/Cache/Adapter/TagAwareAdapter.php
index 62f815e0171a..9110511b9aa7 100644
--- a/src/Symfony/Component/Cache/Adapter/TagAwareAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/TagAwareAdapter.php
@@ -36,7 +36,7 @@ class TagAwareAdapter implements TagAwareAdapterInterface, PruneableInterface, R
     private $knownTagVersions = array();
     private $knownTagVersionsTtl;
 
-    public function __construct(AdapterInterface $itemsPool, AdapterInterface $tagsPool = null, $knownTagVersionsTtl = 0.15)
+    public function __construct(AdapterInterface $itemsPool, AdapterInterface $tagsPool = null, float $knownTagVersionsTtl = 0.15)
     {
         $this->pool = $itemsPool;
         $this->tags = $tagsPool ?: $itemsPool;