diff --git a/src/index.js b/src/index.js
index b56c329..a5c9b7e 100644
--- a/src/index.js
+++ b/src/index.js
@@ -39,6 +39,10 @@ class Vain extends Emitter {
 		});
 
 		this.prefix = `${this.addressFormat.prefix}${this.options.prefix}`;
+
+		if (this.options.keyFormat === 'xpub' && typeof this.options.xpub !== 'string') {
+			throw new Error('An xpub string must be passed in');
+		}
 	}
 
 	generate() {
diff --git a/test/errors.js b/test/errors.js
index c51084c..471ceb2 100644
--- a/test/errors.js
+++ b/test/errors.js
@@ -28,3 +28,9 @@ test('Vain throws when `options.prefix` is `undefined`', t => {
 	const error = t.throws(() => new Vain(options));
 	t.is(error.message, 'Prefix must be set');
 });
+
+test('Vain throws when `options.xpub` is `undefined` when `options.keyFormat` is `xpub`', t => {
+	const options = {keyFormat: 'xpub', prefix: 'BTC'};
+	const error = t.throws(() => new Vain(options));
+	t.is(error.message, 'An xpub string must be passed in');
+});