diff --git a/README.md b/README.md
index bf25fad57..ba15ccb1b 100644
--- a/README.md
+++ b/README.md
@@ -28,7 +28,14 @@ let app = new FastBoot({
   distPath: 'path/to/dist',
   // optional boolean flag when set to true does not reject the promise if there are rendering errors (defaults to false)
   resilient: <boolean>,
-  sandboxGlobals: {...} // optional map of key value pairs to expose in the sandbox
+
+  // optional function used to generate the set of global properties available within the sandbox, receives default globals
+  // and is expected to return an object (the default implementation returns the passed in defaults)
+  buildSandboxGlobals(defaultGlobals) {
+    return Object.assign({}, defaultGlobals, {
+      // additional global properties to define within the sandbox
+    });
+  },
 });
 
 app.visit('/photos', options)
diff --git a/src/ember-app.js b/src/ember-app.js
index 2e578c272..98f258fe4 100644
--- a/src/ember-app.js
+++ b/src/ember-app.js
@@ -29,11 +29,10 @@ class EmberApp {
    * Create a new EmberApp.
    * @param {Object} options
    * @param {string} options.distPath - path to the built Ember application
-   * @param {Object} [options.sandboxGlobals] - sandbox variables that can be added or used for overrides in the sandbox.
+   * @param {Function} [options.buildSandboxGlobals] - the function used to build the final set of global properties accesible within the sandbox
    */
   constructor(options) {
-    // TODO: make these two into builder functions
-    this.sandboxGlobals = options.sandboxGlobals;
+    this.buildSandboxGlobals = options.buildSandboxGlobals || defaultBuildSandboxGlobals;
 
     let distPath = (this.distPath = path.resolve(options.distPath));
     let config = this.readPackageJSON(distPath);
@@ -77,7 +76,7 @@ class EmberApp {
    * Builds and initializes a new sandbox to run the Ember application in.
    */
   buildSandbox() {
-    const { distPath, sandboxGlobals, config, appName, sandboxRequire } = this;
+    const { distPath, buildSandboxGlobals, config, appName, sandboxRequire } = this;
 
     function fastbootConfig(key) {
       if (!key) {
@@ -92,21 +91,19 @@ class EmberApp {
       }
     }
 
-    // add any additional user provided variables or override the default globals in the sandbox
-    let globals = Object.assign(
-      {
-        najax,
-        FastBoot: {
-          require: sandboxRequire,
-          config: fastbootConfig,
-
-          get distPath() {
-            return distPath;
-          },
+    let defaultGlobals = {
+      najax,
+      FastBoot: {
+        require: sandboxRequire,
+        config: fastbootConfig,
+
+        get distPath() {
+          return distPath;
         },
       },
-      sandboxGlobals
-    );
+    };
+
+    let globals = buildSandboxGlobals(defaultGlobals);
 
     return new Sandbox(globals);
   }
@@ -519,4 +516,9 @@ function buildScripts(filePaths) {
     return new vm.Script(source, { filename: filePath });
   });
 }
+
+function defaultBuildSandboxGlobals(defaultGlobals) {
+  return defaultGlobals;
+}
+
 module.exports = EmberApp;
diff --git a/src/index.js b/src/index.js
index 3fbd42640..a82e839a9 100644
--- a/src/index.js
+++ b/src/index.js
@@ -22,31 +22,44 @@ const EmberApp = require('./ember-app');
  *
  * let app = new FastBoot({
  *   distPath: 'path/to/dist',
- *   sandboxGlobals: {...}
+ *   buildSandboxGlobals(globals) {
+ *     return Object.assign({}, globals, {
+ *       // custom globals
+ *     });
+ *   },
  * });
  *
  * app.visit('/photos')
  *   .then(result => result.html())
  *   .then(html => res.send(html));
  */
-
 class FastBoot {
   /**
    * Create a new FastBoot instance.
+   *
    * @param {Object} options
    * @param {string} options.distPath the path to the built Ember application
    * @param {Boolean} [options.resilient=false] if true, errors during rendering won't reject the `visit()` promise but instead resolve to a {@link Result}
-   * @param {Object} [options.sandboxGlobals={}] any additional sandbox variables that an app server wants to override and/or add in the sandbox
+   * @param {Function} [options.buildSandboxGlobals] a function used to build the final set of global properties setup within the sandbox
    */
   constructor(options = {}) {
-    let { distPath, sandboxGlobals } = options;
+    let { distPath, buildSandboxGlobals } = options;
 
     this.resilient = 'resilient' in options ? Boolean(options.resilient) : false;
 
     this.distPath = distPath;
-    this.sandboxGlobals = sandboxGlobals || {};
 
-    this._buildEmberApp(this.distPath, this.sandboxGlobals);
+    // deprecate the legacy path, but support it
+    if (buildSandboxGlobals === undefined && options.sandboxGlobals !== undefined) {
+      console.warn(
+        '[DEPRECATION] Instantiating `fastboot` with a `sandboxGlobals` option has been deprecated. Please migrate to specifying `buildSandboxGlobals` instead.'
+      );
+      buildSandboxGlobals = globals => Object.assign({}, globals, options.sandboxGlobals);
+    }
+
+    this.buildSandboxGlobals = buildSandboxGlobals;
+
+    this._buildEmberApp(this.distPath, this.buildSandboxGlobals);
   }
 
   /**
@@ -92,7 +105,7 @@ class FastBoot {
     this._buildEmberApp(distPath);
   }
 
-  _buildEmberApp(distPath = this.distPath, sandboxGlobals = this.sandboxGlobals) {
+  _buildEmberApp(distPath = this.distPath, buildSandboxGlobals = this.buildSandboxGlobals) {
     if (!distPath) {
       throw new Error(
         'You must instantiate FastBoot with a distPath ' +
@@ -109,7 +122,7 @@ class FastBoot {
 
     this._app = new EmberApp({
       distPath,
-      sandboxGlobals,
+      buildSandboxGlobals,
     });
   }
 }
diff --git a/test/fastboot-test.js b/test/fastboot-test.js
index 41dcdcd05..f77f3c302 100644
--- a/test/fastboot-test.js
+++ b/test/fastboot-test.js
@@ -169,13 +169,15 @@ describe('FastBoot', function() {
       });
   });
 
-  it('can render HTML when sandboxGlobals is provided', function() {
+  it('can render HTML when a custom set of sandbox globals is provided', function() {
     var fastboot = new FastBoot({
       distPath: fixture('custom-sandbox'),
-      sandboxGlobals: {
-        foo: 5,
-        najax: 'undefined',
-        myVar: 'undefined',
+      buildSandboxGlobals(globals) {
+        return Object.assign({}, globals, {
+          foo: 5,
+          najax: 'undefined',
+          myVar: 'undefined',
+        });
       },
     });
 
@@ -256,13 +258,15 @@ describe('FastBoot', function() {
     }
   });
 
-  it('can reload the app using the same sandboxGlobals', function() {
+  it('can reload the app using the same buildSandboxGlobals', function() {
     var fastboot = new FastBoot({
       distPath: fixture('basic-app'),
-      sandboxGlobals: {
-        foo: 5,
-        najax: 'undefined',
-        myVar: 'undefined',
+      buildSandboxGlobals(globals) {
+        return Object.assign({}, globals, {
+          foo: 5,
+          najax: 'undefined',
+          myVar: 'undefined',
+        });
       },
     });