diff --git a/src/transpiler.js b/src/transpiler.js
index 1acd0ba..ec2d90c 100644
--- a/src/transpiler.js
+++ b/src/transpiler.js
@@ -7,8 +7,6 @@
   function getTranspilerModule(loader, globalName) {
     return loader.newModule({ 'default': g[globalName], __useDefault: true });
   }
-  // NB this does not support sub-classing well
-  var firstRun = true;
 
   // use Traceur by default
   Loader.prototype.transpiler = 'traceur';
@@ -17,12 +15,12 @@
     var self = this;
 
     // pick up Transpiler modules from existing globals on first run if set
-    if (firstRun) {
+    if (!self.transpilerHasRun) {
       if (g.traceur && !self.has('traceur'))
         self.set('traceur', getTranspilerModule(self, 'traceur'));
       if (g.babel && !self.has('babel'))
         self.set('babel', getTranspilerModule(self, 'babel'));
-      firstRun = false;
+      self.transpilerHasRun = true;
     }
     
     return self['import'](self.transpiler).then(function(transpiler) {
@@ -101,4 +99,4 @@
   }
 
 
-})(__global.LoaderPolyfill);
\ No newline at end of file
+})(__global.LoaderPolyfill);