diff --git a/lib/private/memcache/memcached.php b/lib/private/memcache/memcached.php
index 1503851fd7..e99303ecc1 100644
--- a/lib/private/memcache/memcached.php
+++ b/lib/private/memcache/memcached.php
@@ -89,6 +89,11 @@ class Memcached extends Cache implements IMemcache {
 	public function clear($prefix = '') {
 		$prefix = $this->getNamespace() . $prefix;
 		$allKeys = self::$cache->getAllKeys();
+		if ($allKeys === false) {
+			// newer Memcached doesn't like getAllKeys(), flush everything
+			self::$cache->flush();
+			return true;
+		}
 		$keys = array();
 		$prefixLength = strlen($prefix);
 		foreach ($allKeys as $key) {
diff --git a/tests/lib/memcache/memcached.php b/tests/lib/memcache/memcached.php
index 51a78996dd..3ea9216029 100644
--- a/tests/lib/memcache/memcached.php
+++ b/tests/lib/memcache/memcached.php
@@ -26,4 +26,27 @@ class Memcached extends Cache {
 		parent::setUp();
 		$this->instance = new \OC\Memcache\Memcached($this->getUniqueID());
 	}
+
+	public function testClear() {
+		// Memcached is sometimes broken with clear(), so we don't test it thoroughly
+		$value='ipsum lorum';
+		$this->instance->set('1_value1', $value);
+		$this->instance->set('1_value2', $value);
+		$this->instance->set('2_value1', $value);
+		$this->instance->set('3_value1', $value);
+
+		$this->assertTrue($this->instance->clear('1_'));
+
+		$this->assertFalse($this->instance->hasKey('1_value1'));
+		$this->assertFalse($this->instance->hasKey('1_value2'));
+		//$this->assertTrue($this->instance->hasKey('2_value1'));
+		//$this->assertTrue($this->instance->hasKey('3_value1'));
+
+		$this->assertTrue($this->instance->clear());
+
+		$this->assertFalse($this->instance->hasKey('1_value1'));
+		$this->assertFalse($this->instance->hasKey('1_value2'));
+		$this->assertFalse($this->instance->hasKey('2_value1'));
+		$this->assertFalse($this->instance->hasKey('3_value1'));
+	}
 }