diff --git a/index.js b/index.js
index c8c9df4..15024e0 100644
--- a/index.js
+++ b/index.js
@@ -6,15 +6,13 @@ var mischief = require('./mischief');
 // prototype defined here.
 var chaos_monkeyware = module.exports = function (options) {
 
-  // Set default values for those not provided by user.
-  options = options || {};
-  options.probability = options.probability || 0.1;
+  var probability = options.probability || 0.1;
 
   return function middleware (req, res, next) {
     var mischiefNames, mischiefName;
 
     // First, decide whether to do anything at all.
-    if (Math.random() > 1 - options.probability) {
+    if (Math.random() > 1 - probability) {
 
       // Select a mischief at random.
       mischiefNames = Object.keys(mischief);
@@ -24,7 +22,7 @@ var chaos_monkeyware = module.exports = function (options) {
       // that this failure was... special.
       res.setHeader('ChaosMonkeyWare', mischiefName);
 
-      if (options.logger) {
+      if (options && typeof options.logger === 'function') {
         options.logger('ChaosMonkeyWare mischief: ' + mischiefName);
       }