diff --git a/src/Core/Cache/Type/MemcacheCache.php b/src/Core/Cache/Type/MemcacheCache.php
index 441c64c3a0..225c338911 100644
--- a/src/Core/Cache/Type/MemcacheCache.php
+++ b/src/Core/Cache/Type/MemcacheCache.php
@@ -68,6 +68,17 @@ class MemcacheCache extends AbstractCache implements ICanCacheInMemory
 		}
 	}
 
+	/**
+	 * Memcache doesn't allow spaces in keys
+	 *
+	 * @param string $key
+	 * @return string
+	 */
+	protected function getCacheKey(string $key): string
+	{
+		return str_replace(' ', '_', parent::getCacheKey($key));
+	}
+
 	/**
 	 * (@inheritdoc)
 	 */
diff --git a/src/Core/Cache/Type/MemcachedCache.php b/src/Core/Cache/Type/MemcachedCache.php
index d86906de76..2d8b4e1c2f 100644
--- a/src/Core/Cache/Type/MemcachedCache.php
+++ b/src/Core/Cache/Type/MemcachedCache.php
@@ -93,6 +93,17 @@ class MemcachedCache extends AbstractCache implements ICanCacheInMemory
 		}
 	}
 
+	/**
+	 * Memcached doesn't allow spaces in keys
+	 *
+	 * @param string $key
+	 * @return string
+	 */
+	protected function getCacheKey(string $key): string
+	{
+		return str_replace(' ', '_', parent::getCacheKey($key));
+	}
+
 	/**
 	 * (@inheritdoc)
 	 */
diff --git a/src/Protocol/OStatus.php b/src/Protocol/OStatus.php
index 90e52d673d..36dbb06c84 100644
--- a/src/Protocol/OStatus.php
+++ b/src/Protocol/OStatus.php
@@ -2017,7 +2017,7 @@ class OStatus
 	 * cache or it is empty
 	 *
 	 * @param string  $owner_nick  Nickname of the feed owner
-	 * @param string  $last_update Date of the last update
+	 * @param string  $last_update Date of the last update (in "Y-m-d H:i:s" format)
 	 * @param integer $max_items   Number of maximum items to fetch
 	 * @param string  $filter      Feed items filter (activity, posts or comments)
 	 * @param boolean $nocache     Wether to bypass caching
diff --git a/tests/src/Core/Cache/CacheTest.php b/tests/src/Core/Cache/CacheTest.php
index 88154c9d22..c249aefbfa 100644
--- a/tests/src/Core/Cache/CacheTest.php
+++ b/tests/src/Core/Cache/CacheTest.php
@@ -237,4 +237,13 @@ abstract class CacheTest extends MockedTest
 		self::assertNotContains('value1', $list);
 		self::assertNotContains('value2', $list);
 	}
+
+	/**
+	 * @small
+	 */
+	public function testSpaceInKey()
+	{
+		self::assertTrue($this->instance->set('key space', 'value'));
+		self::assertEquals('value', $this->instance->get('key space'));
+	}
 }