diff --git a/apps/files_trashbin/lib/Trashbin.php b/apps/files_trashbin/lib/Trashbin.php
index 27242a972d1..035919f55d0 100644
--- a/apps/files_trashbin/lib/Trashbin.php
+++ b/apps/files_trashbin/lib/Trashbin.php
@@ -712,11 +712,13 @@ class Trashbin {
 	 */
 	private static function calculateFreeSpace($trashbinSize, $user) {
 		$config = \OC::$server->getConfig();
-		$systemTrashbinSize = (int)$config->getAppValue('files_trashbin', 'trashbin_size', '-1');
 		$userTrashbinSize = (int)$config->getUserValue($user, 'files_trashbin', 'trashbin_size', '-1');
-		$configuredTrashbinSize = ($userTrashbinSize < 0) ? $systemTrashbinSize : $userTrashbinSize;
-		if ($configuredTrashbinSize) {
-			return $configuredTrashbinSize - $trashbinSize;
+		if ($userTrashbinSize > -1) {
+			return $userTrashbinSize - $trashbinSize;
+		}
+		$systemTrashbinSize = (int)$config->getAppValue('files_trashbin', 'trashbin_size', '-1');
+		if ($systemTrashbinSize > -1) {
+			return $systemTrashbinSize - $trashbinSize;
 		}
 
 		$softQuota = true;
diff --git a/apps/files_trashbin/tests/TrashbinTest.php b/apps/files_trashbin/tests/TrashbinTest.php
index 1e041498390..806a8b765a0 100644
--- a/apps/files_trashbin/tests/TrashbinTest.php
+++ b/apps/files_trashbin/tests/TrashbinTest.php
@@ -120,15 +120,25 @@ class TrashbinTest extends \Test\TestCase {
 		\OC::$server->getAppManager()->enableApp('files_trashbin');
 		$config = \OC::$server->getConfig();
 		$mockConfig = $this->createMock(\OCP\IConfig::class);
-		$mockConfig->expects($this->any())
+		$mockConfig
 			->method('getSystemValue')
-			->will($this->returnCallback(function ($key, $default) use ($config) {
+			->will($this->returnCallback(static function ($key, $default) use ($config) {
 				if ($key === 'filesystem_check_changes') {
 					return \OC\Files\Cache\Watcher::CHECK_ONCE;
 				} else {
 					return $config->getSystemValue($key, $default);
 				}
 			}));
+		$mockConfig
+			->method('getUserValue')
+			->willReturnCallback(static function ($userId, $appName, $key, $default = '') use ($config) {
+				return $config->getUserValue($userId, $appName, $key, $default);
+			});
+		$mockConfig
+			->method('getAppValue')
+			->willReturnCallback(static function ($appName, $key, $default = '') use ($config) {
+				return $config->getAppValue($appName, $key, $default);
+			});
 		$this->overwriteService('AllConfig', $mockConfig);
 
 		$this->trashRoot1 = '/' . self::TEST_TRASHBIN_USER1 . '/files_trashbin';