diff --git a/internal/ui/static/js/webauthn_handler.js b/internal/ui/static/js/webauthn_handler.js
index 2714f4c4..c12c9646 100644
--- a/internal/ui/static/js/webauthn_handler.js
+++ b/internal/ui/static/js/webauthn_handler.js
@@ -42,7 +42,7 @@ class WebAuthnHandler {
         return btoa(String.fromCharCode.apply(null, new Uint8Array(value)))
             .replace(/\+/g, "-")
             .replace(/\//g, "_")
-            .replace(/=/g, "");
+            .replace(/=+$/g, "");
     }
 
     async post(urlKey, username, data) {