diff --git a/dom/apps/src/Webapps.jsm b/dom/apps/src/Webapps.jsm
index 370c2d4f542..3cd08fe02e9 100644
--- a/dom/apps/src/Webapps.jsm
+++ b/dom/apps/src/Webapps.jsm
@@ -937,9 +937,11 @@ this.DOMApplicationRegistry = {
       }
 
       let manifest = new ManifestHelper(aJSON, app.installOrigin);
-      this.downloadPackage(manifest, { manifestURL: aManifestURL,
-                                       origin: app.origin }, isUpdate,
-        function(aId, aManifest) {
+      this.downloadPackage(manifest, {
+          manifestURL: aManifestURL,
+          origin: app.origin,
+          downloadSize: app.downloadSize
+        }, isUpdate, function(aId, aManifest) {
           // Success! Keep the zip in of TmpD, we'll move it out when
           // applyDownload() will be called.
           let tmpDir = FileUtils.getDir("TmpD", ["webapps", aId], true, true);