diff --git a/apps/files_external/lib/Lib/Backend/Local.php b/apps/files_external/lib/Lib/Backend/Local.php
index 88b251360d678..37a4b0458a976 100644
--- a/apps/files_external/lib/Lib/Backend/Local.php
+++ b/apps/files_external/lib/Lib/Backend/Local.php
@@ -26,8 +26,10 @@
 use OCA\Files_External\Lib\Auth\AuthMechanism;
 use OCA\Files_External\Lib\Auth\NullMechanism;
 use OCA\Files_External\Lib\DefinitionParameter;
+use OCA\Files_External\Lib\StorageConfig;
 use OCA\Files_External\Service\BackendService;
 use OCP\IL10N;
+use OCP\IUser;
 
 class Local extends Backend {
 	public function __construct(IL10N $l, NullMechanism $legacyAuth) {
@@ -45,4 +47,8 @@ public function __construct(IL10N $l, NullMechanism $legacyAuth) {
 			->setLegacyAuthMechanism($legacyAuth)
 		;
 	}
+
+	public function manipulateStorageConfig(StorageConfig &$storage, IUser $user = null) {
+		$storage->setBackendOption('isExternal', true);
+	}
 }
diff --git a/lib/private/Files/Storage/Local.php b/lib/private/Files/Storage/Local.php
index fb62a53d89407..8e5c15c523c98 100644
--- a/lib/private/Files/Storage/Local.php
+++ b/lib/private/Files/Storage/Local.php
@@ -51,6 +51,7 @@
 use OCP\Files\GenericFileException;
 use OCP\Files\IMimeTypeDetector;
 use OCP\Files\Storage\IStorage;
+use OCP\Files\StorageNotAvailableException;
 use OCP\IConfig;
 use OCP\Util;
 use Psr\Log\LoggerInterface;
@@ -95,6 +96,12 @@ public function __construct($arguments) {
 
 		// support Write-Once-Read-Many file systems
 		$this->unlinkOnTruncate = $this->config->getSystemValueBool('localstorage.unlink_on_truncate', false);
+
+		if (isset($arguments['isExternal']) && $arguments['isExternal'] && !$this->stat('')) {
+			// data dir not accessible or available, can happen when using an external storage of type Local
+			// on an unmounted system mount point
+			throw new StorageNotAvailableException('Local storage path does not exist "' . $this->getSourcePath('') . '"');
+		}
 	}
 
 	public function __destruct() {
diff --git a/tests/lib/Files/Storage/LocalTest.php b/tests/lib/Files/Storage/LocalTest.php
index e324d2b28db06..1190a2b2da043 100644
--- a/tests/lib/Files/Storage/LocalTest.php
+++ b/tests/lib/Files/Storage/LocalTest.php
@@ -139,4 +139,15 @@ public function testWriteUmaskCopy() {
 		umask($oldMask);
 		$this->assertTrue($this->instance->isUpdatable('test.txt'));
 	}
+
+	public function testUnavailableExternal() {
+		$this->expectException(\OCP\Files\StorageNotAvailableException::class);
+		$this->instance = new \OC\Files\Storage\Local(['datadir' => $this->tmpDir . '/unexist', 'isExternal' => true]);
+	}
+
+	public function testUnavailableNonExternal() {
+		$this->instance = new \OC\Files\Storage\Local(['datadir' => $this->tmpDir . '/unexist']);
+		// no exception thrown
+		$this->assertNotNull($this->instance);
+	}
 }