diff --git a/.gitignore b/.gitignore
index 155f90b..5340214 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,6 @@
 node_modules
-data/
-config.json
-config.js
+/data/
+/config.json
+/config.js
 .env
 .idea/
diff --git a/handlers/middlewares/addedToGroup.js b/handlers/middlewares/addedToGroup.js
index 1efd1e2..fcf6d21 100644
--- a/handlers/middlewares/addedToGroup.js
+++ b/handlers/middlewares/addedToGroup.js
@@ -5,18 +5,14 @@ const { replyOptions } = require('../../bot/options');
 
 const { admin } = require('../../stores/user');
 const { addGroup } = require('../../stores/group');
-const { master } = require('../../config');
+const { isMaster } = require('../../utils/config');
 
 const addedToGroupHandler = async (ctx, next) => {
 	const msg = ctx.message;
-	const isMaster = ctx.from.id === Number(master) ||
-		ctx.from.username &&
-		ctx.from.username.toLowerCase() ===
-		String(master).replace('@', '').toLowerCase();
 
 	const wasAdded = msg.new_chat_members.some(user =>
 		user.username === ctx.me);
-	if (wasAdded && isMaster) {
+	if (wasAdded && isMaster(ctx.from)) {
 		await admin(ctx.from);
 		const link = ctx.chat.username
 			? `https://t.me/${ctx.chat.username.toLowerCase()}`
diff --git a/handlers/middlewares/updateUserData.js b/handlers/middlewares/updateUserData.js
index 886ecc2..c8d5d21 100644
--- a/handlers/middlewares/updateUserData.js
+++ b/handlers/middlewares/updateUserData.js
@@ -1,7 +1,6 @@
 'use strict';
 
-// Config
-const { master } = require('../../config');
+const { isMaster } = require('../../utils/config');
 
 // DB
 const { updateUser } = require('../../stores/user');
@@ -17,11 +16,7 @@ const updateUserDataHandler = async (ctx, next) => {
 
 	ctx.state = {
 		isAdmin: user && user.status === 'admin',
-		isMaster: user &&
-		(user.id === Number(master) ||
-			user.username &&
-			user.username.toLowerCase() ===
-			String(master).replace('@', '').toLowerCase()),
+		isMaster: isMaster(ctx.from),
 		user,
 	};
 
diff --git a/utils/config.js b/utils/config.js
new file mode 100644
index 0000000..f1c4a02
--- /dev/null
+++ b/utils/config.js
@@ -0,0 +1,20 @@
+'use strict';
+
+const config = require('../config');
+const eq = require('./eq');
+
+const masterById = /^\d+$/.test(config.master);
+const masterByUsername = /^@?\w+$/.test(config.master);
+
+if (!masterById && !masterByUsername) {
+	throw new Error('Invalid value for `master` in config file: ' +
+		config.master);
+}
+
+const isMaster = masterById
+	? user => user.id === Number(config.master)
+	: user => user.username && eq.username(user.username, config.master);
+
+module.exports = {
+	isMaster,
+};
diff --git a/utils/eq.js b/utils/eq.js
new file mode 100644
index 0000000..ddb95cb
--- /dev/null
+++ b/utils/eq.js
@@ -0,0 +1,5 @@
+'use strict';
+
+const R = require('ramda');
+
+module.exports = R.map(R.eqBy, require('./normalize'));
diff --git a/utils/normalize.js b/utils/normalize.js
new file mode 100644
index 0000000..fc9ebb6
--- /dev/null
+++ b/utils/normalize.js
@@ -0,0 +1,7 @@
+'use strict';
+
+const username = s => s.replace(/^@/, '').toLowerCase();
+
+module.exports = {
+	username,
+};