diff --git a/tools/catalog.js b/tools/catalog.js
index f51954b316..80ee3a4f83 100644
--- a/tools/catalog.js
+++ b/tools/catalog.js
@@ -448,6 +448,13 @@ _.extend(CompleteCatalog.prototype, {
       // OK, we're building something while uniload
       var ret = {};
       _.each(constraints, function (constraint) {
+        if (_.has(constraint, 'version')) {
+          if (constraint.version !== null) {
+            throw Error("Uniload specifying version? " + JSON.stringify(constraint));
+          }
+          delete constraint.version;
+        }
+
         // Constraints for uniload should just be packages with no version
         // constraint and one local version (since they should all be in core).
         if (!_.has(constraint, 'packageName') || _.size(constraint) !== 1) {
diff --git a/tools/package-loader.js b/tools/package-loader.js
index d22467be7d..cd91aa3eae 100644
--- a/tools/package-loader.js
+++ b/tools/package-loader.js
@@ -14,7 +14,17 @@ exports.PackageLoader = function (options) {
   var self = this;
   if (!options.catalog)
     throw Error("Must specify a catalog");
-  self.versions = options.versions || null;
+
+  self.versions = null;
+  // Ignore specified versions if we're doing this as part of uniload.
+  // The PackageLoader created in uniload.js will not specify a versions option,
+  // but other PackageLoaders (eg, created to build plugins in compiler.compile)
+  // might, but we should ignore that since uniload never loads versioned
+  // packages; it only loads precompiled packages (for built releases) or local
+  //packages (from checkout).
+  if (options.versions && options.catalog !== catalog.uniload)
+    self.versions = options.versions;
+
   self.uniloadDir = options.uniloadDir;
   self.constraintSolverOpts = options.constraintSolverOpts;
   self.catalog = options.catalog;