diff --git a/app/Http/Requests/SaveClientPortalSettings.php b/app/Http/Requests/SaveClientPortalSettings.php
index 00a239c590b7..cd81bf7d31dd 100644
--- a/app/Http/Requests/SaveClientPortalSettings.php
+++ b/app/Http/Requests/SaveClientPortalSettings.php
@@ -44,7 +44,7 @@ class SaveClientPortalSettings extends Request
         if (Utils::isNinja()) {
             if ($this->custom_link == 'subdomain') {
                 $subdomain = substr(strtolower($input['subdomain']), 0, MAX_SUBDOMAIN_LENGTH);
-                $input['subdomain'] = preg_replace('/[^a-zA-Z0-9\-\.]/', '', $subdomain);
+                $input['subdomain'] = preg_replace('/[^a-zA-Z0-9_\-\.]/', '', $subdomain);
                 $input['iframe_url'] = null;
             } else {
                 $iframeURL = substr(strtolower($input['iframe_url']), 0, MAX_IFRAME_URL_LENGTH);
diff --git a/resources/views/accounts/client_portal.blade.php b/resources/views/accounts/client_portal.blade.php
index 39f87c11e07a..00e998d4b251 100644
--- a/resources/views/accounts/client_portal.blade.php
+++ b/resources/views/accounts/client_portal.blade.php
@@ -456,7 +456,7 @@ iframe.src = '{{ rtrim(SITE_URL ,'/') }}/view/'
         var input = $('#subdomain');
         var val = input.val();
         if (!val) return;
-        val = val.replace(/[^a-zA-Z0-9\-]/g, '').toLowerCase().substring(0, {{ MAX_SUBDOMAIN_LENGTH }});
+        val = val.replace(/[^a-zA-Z0-9_\-]/g, '').toLowerCase().substring(0, {{ MAX_SUBDOMAIN_LENGTH }});
         input.val(val);
     }