diff --git a/lib/finalize-manifest.js b/lib/finalize-manifest.js
index 7ebb16f..a5ebe64 100644
--- a/lib/finalize-manifest.js
+++ b/lib/finalize-manifest.js
@@ -25,6 +25,7 @@ function finalizeManifest (pkg, spec, opts, cb) {
 
 module.exports.Manifest = Manifest
 function Manifest (pkg, fromTarball) {
+  fromTarball = fromTarball || {}
   this.name = pkg.name
   this.version = pkg.version
   this.dependencies = pkg.dependencies || {}