diff --git a/README.md b/README.md
index 37f2c65..d36536f 100644
--- a/README.md
+++ b/README.md
@@ -135,6 +135,15 @@ b.transform(envify({
 }))
 ```
 
+## Throw or Warn if env variable is missing ##
+
+May be you want to be sure, that all `process.env` were replaced. There is two
+additional subargs to help you with that: `error` and `warn`.
+
+You can use it in the same way as `purge` subarg.
+
+Keep in mind that `purge`, `error` and `warn` are mutual exclusive.
+
 ## Contributors ##
 
 * [hughsk](http://github.com/hughsk)
diff --git a/test.js b/test.js
index 8ed7ed3..c045957 100644
--- a/test.js
+++ b/test.js
@@ -153,3 +153,39 @@ test('-t [ envify purge --argument ]', function(t) {
       , 'var y = process.env.argument'
     ].join('\n'))
 })
+
+test('-t [ envify error ]', function(t) {
+  var stream = envify()
+  var buffer = ''
+  var caughtError = false;
+
+  stream(__filename, { _: ['error'] })
+    .on('data', function(d) { buffer += d })
+    .on('error', function (e) {
+      t.ok(e, 'throws error if env variable is missing');
+      t.end();
+    })
+    .on('end', function () {
+      t.fail('should throw error if env variable is missing')
+      t.end();
+    })
+    .end('var x = process.env.MISSING_VAR')
+})
+
+test('-t [ envify error --argument]', function(t) {
+  var stream = envify()
+  var buffer = ''
+  var caughtError = false;
+
+  stream(__filename, { _: ['error'], argument: 1 })
+    .on('data', function(d) { buffer += d })
+    .on('error', function (e) {
+      t.fail(e, 'should not throw if env variable is defined');
+      t.end();
+    })
+    .on('end', function () {
+      t.pass('does not throw error if env variable is defined')
+      t.end();
+    })
+    .end('var x = process.env.argument')
+})
diff --git a/visitors.js b/visitors.js
index 4abff9f..06a576a 100644
--- a/visitors.js
+++ b/visitors.js
@@ -1,9 +1,12 @@
 var Syntax = require('jstransform').Syntax
 var utils = require('jstransform/src/utils')
+var util = require('util')
 
 function create(envs) {
   var args  = [].concat(envs[0]._ || []).concat(envs[1]._ || [])
   var purge = args.indexOf('purge') !== -1
+  var error = args.indexOf('error') !== -1
+  var warn = args.indexOf('warn') !== -1
 
   function visitProcessEnv(traverse, node, path, state) {
     var key = node.property.name
@@ -18,6 +21,10 @@ function create(envs) {
 
     if (purge) {
       replaceEnv(node, state, undefined)
+    } else if (error || warn) {
+      var msg = util.format('envify did not find value for "%s" variable', node.property.name);
+      if(error) throw new Error(msg);
+      else console.log('WARN: ', msg);
     }
 
     return false