diff --git a/src/modules/auth.ts b/src/modules/auth.ts
index 0736da2..aed6df0 100644
--- a/src/modules/auth.ts
+++ b/src/modules/auth.ts
@@ -43,15 +43,33 @@ export function createAuthModule(
         );
       }
 
+      const hostname = window.location.hostname;
+      const isPreview = hostname.startsWith("preview--");
+
+      // Skip redirect if already on login page (but not on preview - preview should redirect to main app)
+      if (window.location.pathname === "/login" && !isPreview) {
+        return;
+      }
+
       // If nextUrl is not provided, use the current URL
       const redirectUrl = nextUrl
         ? new URL(nextUrl, window.location.origin).toString()
         : window.location.href;
 
+      // For preview URLs (preview--*), redirect to main app's login page
+      // but keep from_url pointing to the preview URL
+      let loginBaseUrl = options.appBaseUrl ?? "";
+      if (isPreview) {
+        const mainHostname = hostname.replace(/^preview--/, "");
+        loginBaseUrl = `${window.location.protocol}//${mainHostname}${
+          window.location.port ? ":" + window.location.port : ""
+        }`;
+      }
+
       // Build the login URL
-      const loginUrl = `${
-        options.appBaseUrl ?? ""
-      }/login?from_url=${encodeURIComponent(redirectUrl)}`;
+      const loginUrl = `${loginBaseUrl}/login?from_url=${encodeURIComponent(
+        redirectUrl
+      )}`;
 
       // Redirect to the login page
       window.location.href = loginUrl;