diff --git a/README.md b/README.md
index dd33a6a..c50d4d0 100644
--- a/README.md
+++ b/README.md
@@ -50,13 +50,34 @@ $storage->exists('icanboogie');     // false
 $storage->retrieve('icanboogie');   // null
 ```
 
+### Time To Live
+
+The Time To Live (TTL) of an item is the amount of seconds between when that item is stored and it
+is considered stale.
+
+> **Warning:** [`apc.use_request_time`][] needs to be set to `false` if you want to use that feature
+with APCU.
+
+```php
+<?php
+
+use ICanBoogie\Storage\RunTimeStorage;
+
+$storage = new RunTimeStorage;
+$storage->store('icanboogie', "Yes Sir, I Can Boogie", $ttl = 3);
+$storage->retrieve('icanboogie');   // "Yes Sir, I Can Boogie"
+sleep(4);
+$storage->exists('icanboogie');     // false
+$storage->retrieve('icanboogie');   // null
+```
+
 
 
 
 
-### Use storages like arrays
+### Use storage like arrays
 
-Storage implement the `ArrayAccess` interface and may be accessed as arrays.
+Storage implements the `ArrayAccess` interface and may be accessed as arrays.
 
 ```php
 <?php
@@ -79,7 +100,7 @@ $storage['icanboogie'];            // null
 
 ### Iterate storage keys
 
-Storage implement the `IteratorAggregate` interface and may be used in a `foreach` to
+Storage implements the `IteratorAggregate` interface and may be used in a `foreach` to
 iterate their keys:
 
 ```php
@@ -254,3 +275,4 @@ report in `build/coverag`.
 [ArrayAccess]:       https://icanboogie.org/api/storage/master/class-ICanBoogie.Storage.Storage.ArrayAccess.html
 [StorageCollection]: https://icanboogie.org/api/storage/master/class-ICanBoogie.Storage.StorageCollection.html
 [Docker]:            https://www.docker.com/
+[`apc.use_request_time`]: https://www.php.net/manual/en/apcu.configuration.php#ini.apcu.use-request-time
diff --git a/lib/APCStorage.php b/lib/APCStorage.php
index 7f28d7c..65a6937 100644
--- a/lib/APCStorage.php
+++ b/lib/APCStorage.php
@@ -61,7 +61,7 @@ public function retrieve(string $key)
 	 */
 	public function store(string $key, $data, int $ttl = null): void
 	{
-		apcu_store($this->prefix . $key, $data, $ttl);
+		apcu_store($this->prefix . $key, $data, $ttl ?: 0);
 	}
 
 	/**
diff --git a/lib/FileStorage.php b/lib/FileStorage.php
index e0a9948..216bcd4 100644
--- a/lib/FileStorage.php
+++ b/lib/FileStorage.php
@@ -59,27 +59,27 @@ public function __construct(string $path, Adapter $adapter = null)
 	 */
 	public function exists(string $key): bool
 	{
-		return file_exists($this->format_pathname($key));
+		$pathname = $this->format_pathname($key);
+		$ttl_mark = $this->format_pathname_with_ttl($pathname);
+
+		if (file_exists($ttl_mark) && fileatime($ttl_mark) < time() || !file_exists($pathname))
+		{
+			return false;
+		}
+
+		return file_exists($pathname);
 	}
 
 	/**
 	 * @inheritdoc
-	 *
-	 * @param mixed $default The value returned if the key does not exists. Defaults to `null`.
 	 */
 	public function retrieve(string $key)
 	{
-		$this->check_writable();
-
-		$pathname = $this->format_pathname($key);
-		$ttl_mark = $this->format_pathname_with_ttl($pathname);
-
-		if (file_exists($ttl_mark) && fileatime($ttl_mark) < time() || !file_exists($pathname))
-		{
+		if (!$this->exists($key)) {
 			return null;
 		}
 
-		return $this->read($pathname);
+		return $this->read($this->format_pathname($key));
 	}
 
 	/**
diff --git a/lib/RunTimeStorage.php b/lib/RunTimeStorage.php
index 622ec02..65c6e6e 100644
--- a/lib/RunTimeStorage.php
+++ b/lib/RunTimeStorage.php
@@ -18,13 +18,25 @@ class RunTimeStorage implements Storage, \ArrayAccess
 {
 	use Storage\ArrayAccess;
 
+	/**
+	 * @var array<string, mixed>
+	 */
 	private $values = [];
 
+	/**
+	 * @var array<string, int|null>
+	 */
+	private $until = [];
+
 	/**
 	 * @inheritdoc
 	 */
 	public function exists(string $key): bool
 	{
+		if (isset($this->until[$key]) && $this->until[$key] < time()) {
+			return false;
+		}
+
 		return array_key_exists($key, $this->values);
 	}
 
@@ -42,6 +54,7 @@ public function retrieve(string $key)
 	public function store(string $key, $value, int $ttl = null): void
 	{
 		$this->values[$key] = $value;
+		$this->until[$key] = time() + $ttl;
 	}
 
 	/**
diff --git a/tests/StorageCollectionTest.php b/tests/StorageCollectionTest.php
index 8f6e917..9e85e74 100644
--- a/tests/StorageCollectionTest.php
+++ b/tests/StorageCollectionTest.php
@@ -15,6 +15,8 @@
 
 class StorageCollectionTest extends TestCase
 {
+	use TestStorageTrait;
+
 	/**
 	 * @var StorageCollection
 	 */
@@ -33,14 +35,14 @@ class StorageCollectionTest extends TestCase
 	/**
 	 * @var StorageCollection
 	 */
-	private $collection;
+	private $storage;
 
 	public function setUp()
 	{
 		$this->s1 = $s1 = new RunTimeStorage;
 		$this->s2 = $s2 = new RunTimeStorage;
 		$this->s3 = $s3 = new RunTimeStorage;
-		$this->collection = new StorageCollection([ $s1, $s2, $s3 ]);
+		$this->storage = new StorageCollection([ $s1, $s2, $s3 ]);
 	}
 
 	public function test_store()
@@ -48,11 +50,11 @@ public function test_store()
 		$key = uniqid();
 		$value = uniqid();
 
-		$this->collection->store($key, $value);
+		$this->storage->store($key, $value);
 
 		/* @var $storage Storage */
 
-		foreach([ $this->collection, $this->s1, $this->s2, $this->s3 ] as $storage)
+		foreach([ $this->storage, $this->s1, $this->s2, $this->s3 ] as $storage)
 		{
 			$this->assertTrue($storage->exists($key));
 			$this->assertSame($value, $storage->retrieve($key));
@@ -64,7 +66,7 @@ public function test_update_up()
 		$s1 = $this->s1;
 		$s2 = $this->s2;
 		$s3 = $this->s3;
-		$collection = $this->collection;
+		$collection = $this->storage;
 		$key = uniqid();
 		$value = uniqid();
 
@@ -82,7 +84,7 @@ public function test_eliminate()
 		$s1 = $this->s1;
 		$s2 = $this->s2;
 		$s3 = $this->s3;
-		$collection = $this->collection;
+		$collection = $this->storage;
 		$k1 = uniqid();
 		$v1 = uniqid();
 		$k2 = uniqid();
@@ -113,7 +115,7 @@ public function test_clear()
 		$s1 = $this->s1;
 		$s2 = $this->s2;
 		$s3 = $this->s3;
-		$collection = $this->collection;
+		$collection = $this->storage;
 		$k1 = uniqid();
 		$v1 = uniqid();
 		$k2 = uniqid();
@@ -135,7 +137,7 @@ public function test_clear()
 
 	public function test_array_access()
 	{
-		$collection = $this->collection;
+		$collection = $this->storage;
 		$k = uniqid();
 		$v = uniqid();
 
@@ -150,16 +152,16 @@ public function test_array_access()
 
 	public function test_find_by_type()
 	{
-		$this->assertSame($this->s1, $this->collection->find_by_type(RunTimeStorage::class));
+		$this->assertSame($this->s1, $this->storage->find_by_type(RunTimeStorage::class));
 	}
 
 	public function test_find_by_type_undefined()
 	{
-		$this->assertNull($this->collection->find_by_type(RedisStorage::class));
+		$this->assertNull($this->storage->find_by_type(RedisStorage::class));
 	}
 
 	public function test_iterator()
 	{
-		$this->assertInstanceOf(\Iterator::class, $this->collection->getIterator());
+		$this->assertInstanceOf(\Iterator::class, $this->storage->getIterator());
 	}
 }
diff --git a/tests/TestStorageTrait.php b/tests/TestStorageTrait.php
index c7308d7..f883244 100644
--- a/tests/TestStorageTrait.php
+++ b/tests/TestStorageTrait.php
@@ -49,6 +49,17 @@ public function test_storage()
 		$this->assertNull($s->retrieve($k2));
 	}
 
+	public function test_store_with_ttl()
+	{
+		$storage = $this->storage;
+		$storage->store($key = uniqid(), $value = uniqid(), $ttl = 1);
+		$this->assertTrue($storage->exists($key));
+		$this->assertSame($value, $storage->retrieve($key));
+		sleep($ttl + 1);
+		$this->assertFalse($storage->exists($key));
+		$this->assertNull($storage->retrieve($key));
+	}
+
 	public function test_iterator()
 	{
 		$s = $this->storage;
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index e90c7a9..6a56f6c 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -11,5 +11,8 @@
 
 define('ICanBoogie\Storage\SANDBOX_DIR', __DIR__ . '/sandbox');
 
+// https://www.php.net/manual/en/apcu.configuration.php#ini.apcu.use-request-time
+ini_set('apc.use_request_time', false);
+
 require __DIR__ . '/../vendor/autoload.php';
 require 'TestStorageTrait.php';