diff --git a/src/node.js b/src/node.js
index 5034e31f3c..0f3fb4c45c 100644
--- a/src/node.js
+++ b/src/node.js
@@ -251,6 +251,7 @@ var module = (function () {
     this.filename = filename;
 
     var extension = path.extname(filename) || '.js';
+    if (!extensions[extension]) extension = '.js';
     extensions[extension](this, filename);
     this.loaded = true;
   };
diff --git a/test/fixtures/registerExt.hello.world b/test/fixtures/registerExt.hello.world
new file mode 100644
index 0000000000..0420edca79
--- /dev/null
+++ b/test/fixtures/registerExt.hello.world
@@ -0,0 +1 @@
+exports.test = 'passed'
diff --git a/test/simple/test-module-loading.js b/test/simple/test-module-loading.js
index 9c9cfeb7e2..bdff4a9d2d 100644
--- a/test/simple/test-module-loading.js
+++ b/test/simple/test-module-loading.js
@@ -76,6 +76,8 @@ require.extensions['.test'] = function (module, filename) {
 };
 
 assert.equal(require('../fixtures/registerExt').test, "passed");
+// unknown extension, load as .js
+assert.equal(require('../fixtures/registerExt.hello.world').test, "passed");
 
 common.debug('load custom file types that return non-strings');
 require.extensions['.test'] = function (module, filename) {