diff --git a/src/userdb.js b/src/userdb.js
index 55fb13519..b049459b1 100644
--- a/src/userdb.js
+++ b/src/userdb.js
@@ -166,7 +166,7 @@ function add(userId, user, callback) {
     assert.strictEqual(typeof user.displayName, 'string');
     assert.strictEqual(typeof user.source, 'string');
     assert.strictEqual(typeof user.role, 'string');
-    assert.strictEqual(typeof user.avatar, 'string');
+    assert(Buffer.isBuffer(user.avatar));
     assert.strictEqual(typeof callback, 'function');
 
     const query = 'INSERT INTO users (id, username, password, email, fallbackEmail, salt, resetToken, displayName, source, role, avatar) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)';