diff --git a/server/lib/blueprints/types.ts b/server/lib/blueprints/types.ts
index 0a570ca8b..36175e059 100644
--- a/server/lib/blueprints/types.ts
+++ b/server/lib/blueprints/types.ts
@@ -47,7 +47,7 @@ const healthCheckHostnameSchema = z
                 return true;
             }
             const hostnameRegex =
-                /^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)*[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?$/;
+                /^(?:[a-zA-Z0-9_](?:[a-zA-Z0-9_-]{0,61}[a-zA-Z0-9_])?\.)*[a-zA-Z0-9_](?:[a-zA-Z0-9_-]{0,61}[a-zA-Z0-9_])?$/;
             return hostnameRegex.test(val);
         },
         {