diff --git a/lib/nconf/provider.js b/lib/nconf/provider.js
index 425bc04..a67509f 100644
--- a/lib/nconf/provider.js
+++ b/lib/nconf/provider.js
@@ -62,7 +62,7 @@ var Provider = exports.Provider = function (options) {
 ['defaults', 'overrides'].forEach(function (type) {
   Provider.prototype[type] = function (options) {
     return this.add('literal', options);
-  }
+  };
 });
 
 //
@@ -399,19 +399,24 @@ Provider.prototype.save = function (value, callback) {
 Provider.prototype._execute = function (action, syncLength /* [arguments] */) {
   var args = Array.prototype.slice.call(arguments, 2),
       callback = typeof args[args.length - 1] === 'function' && args.pop(),
+      destructive = ['set', 'clear', 'merge'].indexOf(action) !== -1,
       self = this,
       response;
   
   function runAction (name, next) {
     var store = self.sources[name];
 
+    if (destructive && store.readOnly) {
+      return next();
+    }
+
     return store[action].length > syncLength
       ? store[action].apply(store, args.concat(next))
       : next(null, store[action].apply(store, args));
   }
   
   if (callback) {
-    return async.forEach(Object.keys(self.sources), runAction, function (err) {
+    return async.forEach(Object.keys(this.sources), runAction, function (err) {
       return err ? callback(err) : callback();
     });
   }
@@ -420,6 +425,11 @@ Provider.prototype._execute = function (action, syncLength /* [arguments] */) {
   Object.keys(this.sources).forEach(function (name) {
     if (typeof response === 'undefined') {
       var store = self.sources[name];
+
+      if (destructive && store.readOnly) {
+        return;
+      }
+
       response = store[action].apply(store, args);
     }
   });
diff --git a/lib/nconf/stores/argv.js b/lib/nconf/stores/argv.js
index 62c8381..1e2d4a0 100644
--- a/lib/nconf/stores/argv.js
+++ b/lib/nconf/stores/argv.js
@@ -18,8 +18,9 @@ var util = require('util'),
 var Argv = exports.Argv = function (options) {
   Memory.call(this, options);
 
-  this.type    = 'argv';
-  this.options = options || false;
+  this.type     = 'argv';
+  this.readOnly = true;
+  this.options  = options || false;
 };
 
 // Inherit from the Memory store
@@ -51,9 +52,11 @@ Argv.prototype.loadArgv = function () {
     return;
   }
   
+  this.readOnly = false;
   Object.keys(argv).forEach(function (key) {
     self.set(key, argv[key]);
   });
   
+  this.readOnly = true;
   return this.store;
 };
\ No newline at end of file
diff --git a/lib/nconf/stores/env.js b/lib/nconf/stores/env.js
index fa3ce42..89bffd9 100644
--- a/lib/nconf/stores/env.js
+++ b/lib/nconf/stores/env.js
@@ -17,8 +17,9 @@ var util = require('util'),
 var Env = exports.Env = function (options) {
   Memory.call(this, options);
 
-  this.type = 'env';
-  this.options = options || [];
+  this.type     = 'env';
+  this.readOnly = true;
+  this.options  = options || [];
 };
 
 // Inherit from the Memory store
@@ -40,12 +41,14 @@ Env.prototype.loadSync = function () {
 Env.prototype.loadEnv = function () {
   var self = this;
   
+  this.readOnly = false;
   Object.keys(process.env).filter(function (key) {
     return !self.options.length || self.options.indexOf(key) !== -1;
   }).forEach(function (key) {
     self.set(key, process.env[key]);
   });
-    
+  
+  this.readOnly = true;
   return this.store;
 };
 
diff --git a/lib/nconf/stores/literal.js b/lib/nconf/stores/literal.js
index ff69f63..37a723c 100644
--- a/lib/nconf/stores/literal.js
+++ b/lib/nconf/stores/literal.js
@@ -10,8 +10,10 @@ var util = require('util'),
 
 var Literal = exports.Literal = function Literal (store) {
   Memory.call(this);
-  this.type = 'literal'
-  this.store = store || {};
+  
+  this.type     = 'literal';
+  this.readOnly = true;
+  this.store    = store || {};
 };
 
 // Inherit from Memory store.