diff --git a/ember-cli-build.js b/ember-cli-build.js
index <HASH>..<HASH> 100644
--- a/ember-cli-build.js
+++ b/ember-cli-build.js
@@ -15,6 +15,11 @@ module.exports = function(defaults) {
         outputPath: 'new-relic.js'
       };
       break;
+    case '3':
+      options = {
+        loadExternal: true
+      };
+      break;
   }
 
   var app = new EmberAddon(defaults, {
diff --git a/index.js b/index.js
index <HASH>..<HASH> 100644
--- a/index.js
+++ b/index.js
@@ -25,8 +25,12 @@ module.exports = {
 
     this.newRelicConfig = this.getNewRelicConfig(this.project.config(env).newRelic);
 
-    this.loadExternal = options.loadExternal || this.loadExternal;
-    this.outputPath = options.outputPath || this.outputPath;
+    var loadExternal = this.loadExternal = options.loadExternal || this.loadExternal;
+    var outputPath = this.outputPath = options.outputPath || this.outputPath;
+
+    if (loadExternal && !outputPath) {
+      throw this.ui.writeError(new Error('Cannot load external new-relic script from undefined output'));
+    }
   },
 
   isDevelopingAddon: function() {
Add a 3rd case to include throwing an error if outputPath is undefined but loading an external file is expected.