diff --git a/apps/files/command/scan.php b/apps/files/command/scan.php
index e4d719a8b4..2dca0e0e67 100644
--- a/apps/files/command/scan.php
+++ b/apps/files/command/scan.php
@@ -77,7 +77,11 @@ class Scan extends Command {
 			if (is_object($user)) {
 				$user = $user->getUID();
 			}
-			$this->scanFiles($user, $output);
+			if ($this->userManager->userExists($user)) {
+				$this->scanFiles($user, $output);
+			} else {
+				$output->writeln("<error>Unknown user $user</error>");
+			}
 		}
 	}
 }