diff --git a/client/src/components/auth/AuthModal.tsx b/client/src/components/auth/AuthModal.tsx
index 939793a..35edeae 100644
--- a/client/src/components/auth/AuthModal.tsx
+++ b/client/src/components/auth/AuthModal.tsx
@@ -62,6 +62,8 @@ export default function AuthModal() {
                 <span>Name</span>
                 <input
                   type="text"
+                  pattern="[A-Za-z0-9_]+"
+                  title="Alphanumeric characters and underscores only"
                   id="guestName"
                   name="guestName"
                   placeholder="Enter name here..."