diff --git a/l3build.lua b/l3build.lua
index ccd336e9..dde73c72 100644
--- a/l3build.lua
+++ b/l3build.lua
@@ -190,7 +190,7 @@ psext  = psext  or ".ps"
 tlgext = tlgext or ".tlg"
 
 -- For "manifest"
-manifestfile = "MANIFEST.md"
+manifestfile = manifestfile or "MANIFEST.md"
 
 -- File operations are aided by the LuaFileSystem module
 local lfs = require("lfs")