diff --git a/externs/air/sys/FileSystem.hx b/externs/air/sys/FileSystem.hx
index bd5e31302..e278a1d38 100644
--- a/externs/air/sys/FileSystem.hx
+++ b/externs/air/sys/FileSystem.hx
@@ -37,5 +37,8 @@ class FileSystem
 
 	public static function deleteDirectory(path:String):Void {}
 
-	public static function readDirectory(path:String):Array<String> {}
+	public static function readDirectory(path:String):Array<String>
+	{
+		return null;
+	}
 }