diff --git a/app/(auth)/auth.config.ts b/app/(auth)/auth.config.ts
index 57a473511..d3859dc2a 100644
--- a/app/(auth)/auth.config.ts
+++ b/app/(auth)/auth.config.ts
@@ -1,10 +1,13 @@
 import type { NextAuthConfig } from "next-auth";
+import { isIP } from "node:net";
 
 export function buildAuthConfig(authUrl?: string | null): NextAuthConfig {
   const resolvedAuthUrl = authUrl || process.env.AUTH_URL || "";
   const isSecure = resolvedAuthUrl.startsWith("https://");
   const hostName = resolvedAuthUrl ? new URL(resolvedAuthUrl).hostname : undefined;
-  const cookieDomain = hostName && hostName !== "localhost" ? hostName : undefined;
+  // Browsers may reject `Domain` cookies for IP hosts; keep them host-only in that case.
+  const cookieDomain =
+    hostName && hostName !== "localhost" && isIP(hostName) === 0 ? hostName : undefined;
 
   return {
     trustHost: true,