diff --git a/lib/private/Memcache/Factory.php b/lib/private/Memcache/Factory.php
index ff539e5542..b79f17ba8e 100644
--- a/lib/private/Memcache/Factory.php
+++ b/lib/private/Memcache/Factory.php
@@ -31,8 +31,10 @@
 
 namespace OC\Memcache;
 
-use \OCP\ICacheFactory;
-use \OCP\ILogger;
+use OCP\ICache;
+use OCP\ICacheFactory;
+use OCP\ILogger;
+use OCP\IMemcache;
 
 class Factory implements ICacheFactory {
 	const NULL_CACHE = '\\OC\\Memcache\\NullCache';
@@ -69,7 +71,7 @@ class Factory implements ICacheFactory {
 	 * @param string|null $distributedCacheClass
 	 * @param string|null $lockingCacheClass
 	 */
-	public function __construct($globalPrefix, ILogger $logger,
+	public function __construct(string $globalPrefix, ILogger $logger,
 		$localCacheClass = null, $distributedCacheClass = null, $lockingCacheClass = null)
 	{
 		$this->logger = $logger;
@@ -128,9 +130,9 @@ class Factory implements ICacheFactory {
 	 * create a cache instance for storing locks
 	 *
 	 * @param string $prefix
-	 * @return \OCP\IMemcache
+	 * @return IMemcache
 	 */
-	public function createLocking($prefix = '') {
+	public function createLocking(string $prefix = ''): IMemcache {
 		return new $this->lockingCacheClass($this->globalPrefix . '/' . $prefix);
 	}
 
@@ -138,9 +140,9 @@ class Factory implements ICacheFactory {
 	 * create a distributed cache instance
 	 *
 	 * @param string $prefix
-	 * @return \OC\Memcache\Cache
+	 * @return ICache
 	 */
-	public function createDistributed($prefix = '') {
+	public function createDistributed(string $prefix = ''): ICache {
 		return new $this->distributedCacheClass($this->globalPrefix . '/' . $prefix);
 	}
 
@@ -148,18 +150,19 @@ class Factory implements ICacheFactory {
 	 * create a local cache instance
 	 *
 	 * @param string $prefix
-	 * @return \OC\Memcache\Cache
+	 * @return ICache
 	 */
-	public function createLocal($prefix = '') {
+	public function createLocal(string $prefix = ''): ICache {
 		return new $this->localCacheClass($this->globalPrefix . '/' . $prefix);
 	}
 
 	/**
 	 * @see \OC\Memcache\Factory::createDistributed()
 	 * @param string $prefix
-	 * @return \OC\Memcache\Cache
+	 * @return ICache
+	 * @deprecated 13.0.0 Use either createLocking, createDistributed or createLocal
 	 */
-	public function create($prefix = '') {
+	public function create(string $prefix = ''): ICache {
 		return $this->createDistributed($prefix);
 	}
 
@@ -168,16 +171,16 @@ class Factory implements ICacheFactory {
 	 *
 	 * @return bool
 	 */
-	public function isAvailable() {
+	public function isAvailable(): bool {
 		return ($this->distributedCacheClass !== self::NULL_CACHE);
 	}
 
 	/**
 	 * @see \OC\Memcache\Factory::createLocal()
 	 * @param string $prefix
-	 * @return Cache
+	 * @return ICache
 	 */
-	public function createLowLatency($prefix = '') {
+	public function createLowLatency(string $prefix = ''): ICache {
 		return $this->createLocal($prefix);
 	}
 
@@ -186,7 +189,7 @@ class Factory implements ICacheFactory {
 	 *
 	 * @return bool
 	 */
-	public function isAvailableLowLatency() {
+	public function isAvailableLowLatency(): bool {
 		return ($this->localCacheClass !== self::NULL_CACHE);
 	}
 }
diff --git a/lib/public/ICacheFactory.php b/lib/public/ICacheFactory.php
index cc4d8fa3ec..76145fe1f7 100644
--- a/lib/public/ICacheFactory.php
+++ b/lib/public/ICacheFactory.php
@@ -1,4 +1,5 @@
 <?php
+declare(strict_types=1);
 /**
  * @copyright Copyright (c) 2016, ownCloud, Inc.
  *
@@ -36,11 +37,11 @@ interface ICacheFactory{
 	 * All entries added trough the cache instance will be namespaced by $prefix to prevent collisions between apps
 	 *
 	 * @param string $prefix
-	 * @return \OCP\ICache
+	 * @return ICache
 	 * @since 7.0.0
 	 * @deprecated 13.0.0 Use either createLocking, createDistributed or createLocal
 	 */
-	public function create($prefix = '');
+	public function create(string $prefix = ''): ICache;
 
 	/**
 	 * Check if any memory cache backend is available
@@ -48,32 +49,32 @@ interface ICacheFactory{
 	 * @return bool
 	 * @since 7.0.0
 	 */
-	public function isAvailable();
+	public function isAvailable(): bool;
 
 	/**
 	 * create a cache instance for storing locks
 	 *
 	 * @param string $prefix
-	 * @return \OCP\IMemcache
+	 * @return IMemcache
 	 * @since 13.0.0
 	 */
-	public function createLocking($prefix = '');
+	public function createLocking(string $prefix = ''): IMemcache;
 
 	/**
 	 * create a distributed cache instance
 	 *
 	 * @param string $prefix
-	 * @return \OCP\ICache
+	 * @return ICache
 	 * @since 13.0.0
 	 */
-	public function createDistributed($prefix = '');
+	public function createDistributed(string $prefix = ''): ICache;
 
 	/**
 	 * create a local cache instance
 	 *
 	 * @param string $prefix
-	 * @return \OCP\ICache
+	 * @return ICache
 	 * @since 13.0.0
 	 */
-	public function createLocal($prefix = '');
+	public function createLocal(string $prefix = ''): ICache;
 }
diff --git a/tests/lib/Memcache/FactoryTest.php b/tests/lib/Memcache/FactoryTest.php
index ce6c25cd87..1944b1bd35 100644
--- a/tests/lib/Memcache/FactoryTest.php
+++ b/tests/lib/Memcache/FactoryTest.php
@@ -20,9 +20,10 @@
  */
 namespace Test\Memcache;
 
+use OC\Memcache\NullCache;
 use OCP\ILogger;
 
-class Test_Factory_Available_Cache1 {
+class Test_Factory_Available_Cache1 extends NullCache {
 	public function __construct($prefix = '') {
 	}
 
@@ -31,7 +32,7 @@ class Test_Factory_Available_Cache1 {
 	}
 }
 
-class Test_Factory_Available_Cache2 {
+class Test_Factory_Available_Cache2 extends NullCache {
 	public function __construct($prefix = '') {
 	}
 
@@ -40,7 +41,7 @@ class Test_Factory_Available_Cache2 {
 	}
 }
 
-class Test_Factory_Unavailable_Cache1 {
+class Test_Factory_Unavailable_Cache1 extends NullCache {
 	public function __construct($prefix = '') {
 	}
 
@@ -49,7 +50,7 @@ class Test_Factory_Unavailable_Cache1 {
 	}
 }
 
-class Test_Factory_Unavailable_Cache2 {
+class Test_Factory_Unavailable_Cache2 extends NullCache {
 	public function __construct($prefix = '') {
 	}