diff --git a/README.md b/README.md
index 0a38ee4..1cb517e 100644
--- a/README.md
+++ b/README.md
@@ -42,3 +42,9 @@ I believe all the above said tools will be available in a typical UNIX machine.
 # Configurations
 
 Please check config.js. All config values can be over-written by `environment-variables` 
+
+# Using npm-offline-registry as a completely isolated registry
+
+If you set the ``ENABLE_NPM_FAILOVER`` config value to ``false`` then npm-offlin-registry will not attempt to
+contact the upstream NPM registry for unknown packages and instead return a 404 response, meaning you can use
+it as an alternative to the NPM registry behind a firewall / isolated from the internet.
diff --git a/app.js b/app.js
index df8b2d2..3885808 100644
--- a/app.js
+++ b/app.js
@@ -4,6 +4,7 @@ var utils = require( __dirname + '/./utils');
 
 var NPM_PATH = config.NPM_PATH;
 var REGISTRY_NAME = config.REGISTRY_NAME;
+var ENABLE_NPM_FAILOVER = config.ENABLE_NPM_FAILOVER;
 
 
 var fetchAndCacheMetadata = utils.fetchAndCacheMetadata;
@@ -36,8 +37,12 @@ app.get( '/:package', function( req, res, next ){
   return fileExists( cacheFile )
     .tap( function( isExists ){
       if( !isExists ){
-        res._log.cacheHit = '---';
-        return fetchAndCacheMetadata( packageName, cacheFile );
+        if ( ENABLE_NPM_FAILOVER ) {
+          res._log.cacheHit = '---';
+          return fetchAndCacheMetadata( packageName, cacheFile );
+        } else {
+          return res.status( 404 ).json( {} );
+        }
       }
     })
     .then( function( ){
@@ -60,8 +65,12 @@ app.get( '/:package/-/:tarball', function( req, res, next ){
   fileExists( packagePath )
     .tap( function( isExists ){
       if( !isExists ){
-        res._log.cacheHit = '---';
-        return fetchAndCacheTarball( packageName, version, packagePath );
+        if ( ENABLE_NPM_FAILOVER ) {
+          res._log.cacheHit = '---';
+          return fetchAndCacheTarball( packageName, version, packagePath );
+        } else {
+          return res.status( 404 ).json( {} );
+        }
       }
     })
     .then( function(){
diff --git a/config.js b/config.js
index 0c153cd..95c98ff 100644
--- a/config.js
+++ b/config.js
@@ -2,7 +2,8 @@
 var defaultConfig = {
   NPM_PATH       : process.env.HOME + '/.npm',
   REGISTRY_NAME  : 'registry.npmjs.org',
-  PORT: 8234
+  PORT: 8234,
+  ENABLE_NPM_FAILOVER: true
 };
 
 var config = {};