diff --git a/api/src/Vfs/StreamWrapper.php b/api/src/Vfs/StreamWrapper.php
index f4864904f8..53995e7b30 100644
--- a/api/src/Vfs/StreamWrapper.php
+++ b/api/src/Vfs/StreamWrapper.php
@@ -301,7 +301,7 @@ class StreamWrapper implements StreamWrapperIface
 		{
 			return false;
 		}
-		if ($mode != 'r' && self::url_is_readonly($url))
+		if (str_replace('b', '', $mode) != 'r' && self::url_is_readonly($url))
 		{
 			return false;
 		}