diff --git a/apps/files_external/lib/streamwrapper.php b/apps/files_external/lib/streamwrapper.php
index 4a63dfb6e0277b6c6fd9d5286fe7a42257ba7f9f..a086f411f573b0005c53d82ca9df9e1699687043 100644
--- a/apps/files_external/lib/streamwrapper.php
+++ b/apps/files_external/lib/streamwrapper.php
@@ -42,11 +42,16 @@ abstract class StreamWrapper extends Common {
 	}
 
 	public function isReadable($path) {
-		return true; //not properly supported
+		// at least check whether it exists
+		// subclasses might want to implement this more thoroughly
+		return $this->file_exists($path);
 	}
 
 	public function isUpdatable($path) {
-		return true; //not properly supported
+		// at least check whether it exists
+		// subclasses might want to implement this more thoroughly
+		// a non-existing file/folder isn't updatable
+		return $this->file_exists($path);
 	}
 
 	public function file_exists($path) {