diff --git a/lib/config.js b/lib/config.js
index cacecb92c..708907edd 100644
--- a/lib/config.js
+++ b/lib/config.js
@@ -123,7 +123,7 @@ var normalizeConfig = function(config) {
 
 
 var readConfigFile = function(filepath) {
-  var configEnv = {
+  var initSandbox = {
     // constants
     LOG_DISABLE: constant.LOG_DISABLE,
     LOG_ERROR:   constant.LOG_ERROR,
@@ -137,7 +137,7 @@ var readConfigFile = function(filepath) {
     __filename: filepath,
     __dirname: path.dirname(filepath)
   };
-
+  var configEnv = vm.createContext(initSandbox);
 
   // TODO(vojta): remove
   var CONST_ERR = '%s is not supported anymore.\n\tPlease use `frameworks = ["%s"];` instead.';
@@ -169,7 +169,7 @@ var readConfigFile = function(filepath) {
       configSrc = coffee.compile(configSrc.toString(), {bare: true});
     }
 
-    vm.runInNewContext(configSrc, configEnv);
+    vm.runInContext(configSrc, configEnv);
   } catch(e) {
     if (e.name === 'SyntaxError') {
       log.error('Syntax error in config file!\n' + e.message);
@@ -181,6 +181,11 @@ var readConfigFile = function(filepath) {
 
     process.exit(1);
   }
+  
+  // Clean up the env before we return it.
+  for (var i in initSandbox) {
+    delete configEnv[i];
+  }
 
   return configEnv;
 };
@@ -228,11 +233,12 @@ var parseConfig = function(configFilePath, cliOptions) {
   };
 
   // merge the config from config file and cliOptions (precendense)
+  Object.getOwnPropertyNames(configFromFile).forEach(function(key) {
+    config[key] = configFromFile[key];
+  });
   Object.getOwnPropertyNames(config).forEach(function(key) {
     if (cliOptions.hasOwnProperty(key)) {
       config[key] = cliOptions[key];
-    } else if (configFromFile.hasOwnProperty(key)) {
-      config[key] = configFromFile[key];
     }
   });