diff --git a/src/Core/Cache/ArrayCache.php b/src/Core/Cache/ArrayCache.php
index 5add98cc2a..c6f3983ee2 100644
--- a/src/Core/Cache/ArrayCache.php
+++ b/src/Core/Cache/ArrayCache.php
@@ -21,7 +21,7 @@ class ArrayCache extends Cache implements IMemoryCache
 	 */
 	public function getAllKeys($prefix = null)
 	{
-		return $this->filterArrayKeysByPrefix($this->cachedData, $prefix);
+		return $this->filterArrayKeysByPrefix(array_keys($this->cachedData), $prefix);
 	}
 
 	/**
diff --git a/src/Core/Cache/Cache.php b/src/Core/Cache/Cache.php
index b40c129ae7..cf5b15d052 100644
--- a/src/Core/Cache/Cache.php
+++ b/src/Core/Cache/Cache.php
@@ -84,19 +84,19 @@ abstract class Cache implements ICache
 	 * Filters the keys of an array with a given prefix
 	 * Returns the filtered keys as an new array
 	 *
-	 * @param array $array The array, which should get filtered
+	 * @param array $keys The keys, which should get filtered
 	 * @param string|null $prefix The prefix (if null, all keys will get returned)
 	 *
 	 * @return array The filtered array with just the keys
 	 */
-	protected function filterArrayKeysByPrefix($array, $prefix = null)
+	protected function filterArrayKeysByPrefix(array $keys, string $prefix = null)
 	{
 		if (empty($prefix)) {
-			return array_keys($array);
+			return $keys;
 		} else {
 			$result = [];
 
-			foreach (array_keys($array) as $key) {
+			foreach ($keys as $key) {
 				if (strpos($key, $prefix) === 0) {
 					array_push($result, $key);
 				}
diff --git a/src/Core/Cache/MemcachedCache.php b/src/Core/Cache/MemcachedCache.php
index ac0648a6ce..89685c3f25 100644
--- a/src/Core/Cache/MemcachedCache.php
+++ b/src/Core/Cache/MemcachedCache.php
@@ -27,6 +27,17 @@ class MemcachedCache extends Cache implements IMemoryCache
 	 */
 	private $logger;
 
+	/**
+	 * @var string First server address
+	 */
+
+	private $firstServer;
+
+	/**
+	 * @var int First server port
+	 */
+	private $firstPort;
+
 	/**
 	 * Due to limitations of the INI format, the expected configuration for Memcached servers is the following:
 	 * array {
@@ -58,6 +69,9 @@ class MemcachedCache extends Cache implements IMemoryCache
 			}
 		});
 
+		$this->firstServer = $memcached_hosts[0][0] ?? 'localhost';
+		$this->firstPort   = $memcached_hosts[0][1] ?? 11211;
+
 		$this->memcached->addServers($memcached_hosts);
 
 		if (count($this->memcached->getServerList()) == 0) {
@@ -70,14 +84,94 @@ class MemcachedCache extends Cache implements IMemoryCache
 	 */
 	public function getAllKeys($prefix = null)
 	{
-		$keys = $this->getOriginalKeys($this->memcached->getAllKeys());
+		$keys = $this->getOriginalKeys($this->getMemcachedKeys());
 
-		if ($this->memcached->getResultCode() == Memcached::RES_SUCCESS) {
-			return $this->filterArrayKeysByPrefix($keys, $prefix);
-		} else {
-			$this->logger->debug('Memcached \'getAllKeys\' failed', ['result' => $this->memcached->getResultMessage()]);
-			return [];
+		return $this->filterArrayKeysByPrefix($keys, $prefix);
+	}
+
+	/**
+	 * Get all memcached keys.
+	 * Special function because getAllKeys() is broken since memcached 1.4.23.
+	 *
+	 * cleaned up version of code found on Stackoverflow.com by Maduka Jayalath
+	 *
+	 * @return array|int - all retrieved keys (or negative number on error)
+	 */
+	private function getMemcachedKeys()
+	{
+		$mem = @fsockopen($this->firstServer, $this->firstPort);
+		if ($mem === false) {
+			return -1;
 		}
+
+		// retrieve distinct slab
+		$r = @fwrite($mem, 'stats items' . chr(10));
+		if ($r === false) {
+			return -2;
+		}
+
+		$slab = [];
+		while (($l = @fgets($mem, 1024)) !== false) {
+			// finished?
+			$l = trim($l);
+			if ($l == 'END') {
+				break;
+			}
+
+			$m = [];
+			// <STAT items:22:evicted_nonzero 0>
+			$r = preg_match('/^STAT\sitems\:(\d+)\:/', $l, $m);
+			if ($r != 1) {
+				return -3;
+			}
+			$a_slab = $m[1];
+
+			if (!array_key_exists($a_slab, $slab)) {
+				$slab[$a_slab] = [];
+			}
+		}
+
+		reset($slab);
+		foreach ($slab as $a_slab_key => &$a_slab) {
+			$r = @fwrite($mem, 'stats cachedump ' . $a_slab_key . ' 100' . chr(10));
+			if ($r === false) {
+				return -4;
+			}
+
+			while (($l = @fgets($mem, 1024)) !== false) {
+				// finished?
+				$l = trim($l);
+				if ($l == 'END') {
+					break;
+				}
+
+				$m = [];
+				// ITEM 42 [118 b; 1354717302 s]
+				$r = preg_match('/^ITEM\s([^\s]+)\s/', $l, $m);
+				if ($r != 1) {
+					return -5;
+				}
+				$a_key = $m[1];
+
+				$a_slab[] = $a_key;
+			}
+		}
+
+		// close the connection
+		@fclose($mem);
+		unset($mem);
+
+		$keys = [];
+		reset($slab);
+		foreach ($slab AS &$a_slab) {
+			reset($a_slab);
+			foreach ($a_slab AS &$a_key) {
+				$keys[] = $a_key;
+			}
+		}
+		unset($slab);
+
+		return $keys;
 	}
 
 	/**
diff --git a/src/Core/Lock/DatabaseLock.php b/src/Core/Lock/DatabaseLock.php
index 2f409cd3d2..07cf88c494 100644
--- a/src/Core/Lock/DatabaseLock.php
+++ b/src/Core/Lock/DatabaseLock.php
@@ -138,7 +138,7 @@ class DatabaseLock extends Lock
 		if (empty($prefix)) {
 			$where = ['`expires` >= ?', DateTimeFormat::utcNow()];
 		} else {
-			$where = ['`expires` >= ? AND `k` LIKE CONCAT(?, \'%\')', DateTimeFormat::utcNow(), $prefix];
+			$where = ['`expires` >= ? AND `name` LIKE CONCAT(?, \'%\')', DateTimeFormat::utcNow(), $prefix];
 		}
 
 		$stmt = $this->dba->select('locks', ['name'], $where);
diff --git a/tests/src/Core/Cache/CacheTest.php b/tests/src/Core/Cache/CacheTest.php
index 92fdaffa32..9071a55c40 100644
--- a/tests/src/Core/Cache/CacheTest.php
+++ b/tests/src/Core/Cache/CacheTest.php
@@ -2,7 +2,6 @@
 
 namespace Friendica\Test\src\Core\Cache;
 
-use Friendica\Core\Cache\MemcachedCache;
 use Friendica\Test\MockedTest;
 use Friendica\Util\PidFile;
 
@@ -202,10 +201,6 @@ abstract class CacheTest extends MockedTest
 	 */
 	public function testGetAllKeys($value1, $value2, $value3)
 	{
-		if ($this->cache instanceof MemcachedCache) {
-			$this->markTestSkipped('Memcached doesn\'t support getAllKeys anymore');
-		}
-
 		$this->assertTrue($this->instance->set('value1', $value1));
 		$this->assertTrue($this->instance->set('value2', $value2));
 		$this->assertTrue($this->instance->set('test_value3', $value3));
@@ -219,5 +214,7 @@ abstract class CacheTest extends MockedTest
 		$list = $this->instance->getAllKeys('test');
 
 		$this->assertContains('test_value3', $list);
+		$this->assertNotContains('value1', $list);
+		$this->assertNotContains('value2', $list);
 	}
 }