diff --git a/forge/routes/setup/index.js b/forge/routes/setup/index.js
index 1ad5692ad5..248543a9fd 100644
--- a/forge/routes/setup/index.js
+++ b/forge/routes/setup/index.js
@@ -80,7 +80,7 @@ module.exports = async function (app) {
             reply.code(404).send()
             return
         }
-        if (/^(admin|root)$/.test(request.body.username) || !/^[a-z0-9-_]+$/.test(request.body.username)) {
+        if (/^(admin|root)$/.test(request.body.username) || !/^[a-z0-9-_]+$/i.test(request.body.username)) {
             reply.code(400).send({ error: 'invalid username' })
             return
         }
diff --git a/frontend/src/pages/setup/CreateAdminUser.vue b/frontend/src/pages/setup/CreateAdminUser.vue
index 4e31858f8f..ba41b7b485 100644
--- a/frontend/src/pages/setup/CreateAdminUser.vue
+++ b/frontend/src/pages/setup/CreateAdminUser.vue
@@ -81,7 +81,7 @@ export default {
     watch: {
         'input.username': function (v) {
             if (v && !/^[a-z0-9-_]+$/i.test(v)) {
-                this.errors.username = 'Must only contain a-z 0-9 - _'
+                this.errors.username = 'Must only contain a-z A-Z 0-9 - _'
             } else {
                 this.errors.username = ''
             }