diff --git a/lib/nlogger.js b/lib/nlogger.js
index fb032de..65ef6c2 100644
--- a/lib/nlogger.js
+++ b/lib/nlogger.js
@@ -68,7 +68,8 @@ function getClass(module) {
 				return 'main';
 			} else {
 				if (fs.existsSync(module.id)) { // module.id is file path
-					return path.relative(path.dirname(require.main.filename), path.dirname(module.id)) + path.sep + path.basename(module.id, '.js');
+					var entryPoint = (require.main && require.main.filename) || '';
+					return path.relative(path.dirname(entryPoint), path.dirname(module.id)) + path.sep + path.basename(module.id, '.js');
 				}
 				return module.id;
 			}