diff --git a/tools/catalog.js b/tools/catalog.js
index b8424589f5..fa87ed01cb 100644
--- a/tools/catalog.js
+++ b/tools/catalog.js
@@ -252,12 +252,16 @@ _.extend(Catalog.prototype, {
   //
   // Doesn't download packages. Downloading should be done at the time
   // that .meteor/versions is updated.
+  //
+  // HACK: Version can be null if you are certain that the package is to be
+  // loaded from local packages. In the future, version should always be
+  // required and we should confirm that the version on disk is the version that
+  // we asked for. This is to support unipackage loader not having a version
+  // manifest.
   getLoadPathForPackage: function (name, version) {
     var self = this;
 
     if (_.has(self.effectiveLocalPackages, name)) {
-      // XXX should confirm that the version on disk actually matches
-      // the requested version
       return self.effectiveLocalPackages[name];
     }
 
diff --git a/tools/package-loader.js b/tools/package-loader.js
index 7d1a78e6a4..fdcb69082c 100644
--- a/tools/package-loader.js
+++ b/tools/package-loader.js
@@ -5,7 +5,8 @@ var catalog = require('./catalog.js');
 var packageLoader = exports;
 
 // options:
-//   versions: a map from package name to the version to use
+//  - versions: a map from package name to the version to use.  or null to only
+//    use local packages and ignore the package versions.
 packageLoader.PackageLoader = function (options) {
   var self = this;
   self.versions = options.versions;
@@ -37,11 +38,17 @@ _.extend(packageLoader.PackageLoader, {
       options.throwOnError = true;
     }
 
-    if (! _.has(self.versions, name))
+    if (! self.versions && ! _.has(self.versions, name))
       throw new Error("no version chosen for package?");
 
-    var loadPath = catalog.getLoadPathForPackage(name,
-                                                 self.versions[name]);
+    var version;
+    if (self.versions) {
+      version = self.versions[name];
+    } else {
+      version = null;
+    }
+
+    var loadPath = catalog.getLoadPathForPackage(name, version);
     if (! loadPath) {
       if (options.throwOnError === false)
         return null;
@@ -72,5 +79,5 @@ _.extend(packageLoader.PackageLoader, {
       return [pkg.getSingleSlice(spec.slice, arch)];
     else
       return pkg.getDefaultSlices(arch);
-  },
+  }
 });
diff --git a/tools/unipackage.js b/tools/unipackage.js
index a1b819f7cb..1954754a51 100644
--- a/tools/unipackage.js
+++ b/tools/unipackage.js
@@ -3,7 +3,7 @@ var library = require('./library.js');
 var bundler = require('./bundler.js');
 var buildmessage = require('./buildmessage.js');
 var release = require('./release.js');
-var PackageLoader = require("./package-loader.js");
+var PackageLoader = require("./package-loader.js").PackageLoader;
 var packageCache = require("./package-cache.js");
 
 // Load unipackages into the currently running node.js process. Use
@@ -80,10 +80,8 @@ var load = function (options) {
     title: "loading unipackage"
   }, function () {
     // Load the code
-    // #RunningTheConstraintSolverToBuildAPackage ???
-    var versions = { }; // XXX XXX actually run the constraint solver!
-    var loader = new PackageLoader.PackageLoader({
-      versions: versions
+    var loader = new PackageLoader({
+      versions: null
     });
 
     var image = bundler.buildJsImage({