diff --git a/.env.example b/.env.example
index 031cddd6..c89143a5 100644
--- a/.env.example
+++ b/.env.example
@@ -13,6 +13,10 @@ SUPABASE_SERVICE_ROLE_KEY=YOUR_SERVICE_ROLE_KEY
 MAXMIND_LICENSE_KEY=
 MAXMIND_GEOLITE2_CITY_DB_PATH=data/GeoLite2-City.mmdb
 
+# Ad network: slot credited when a serving request names none (a bare curl of
+# /api/ads/motd). Without it, slotless requests can only return the house ad.
+ADS_DEFAULT_SLOT_ID=
+
 # CoinPay credit purchases
 COINPAY_MERCHANT_ID=merchant_xxx
 COINPAY_API_KEY=cp_xxx
diff --git a/app/api/ads/motd/route.ts b/app/api/ads/motd/route.ts
index a55db6b8..300ae496 100644
--- a/app/api/ads/motd/route.ts
+++ b/app/api/ads/motd/route.ts
@@ -8,6 +8,11 @@
 // — anywhere an <iframe> can't go. Impressions are metered server-side by
 // serveAd, exactly like the HTML paths; an unknown or inactive slot falls back
 // to the (unmetered) CrawlProof house ad so a login banner is never blank.
+//
+// `slot` identifies the publisher placement being filled — that's who the
+// impression and any click earnings are credited to. Omitting it (a bare curl
+// of this URL) uses ADS_DEFAULT_SLOT_ID, the network's own slot, so the
+// endpoint still rotates real campaigns on every load.
 
 import { NextRequest, NextResponse } from "next/server";
 import { serveAd } from "@/lib/ads/serve";
@@ -16,6 +21,7 @@ import { TERMINAL_FORMAT_ID } from "@/lib/ads/formats";
 import { clampCols, renderCreativeText, terminalDeviceType } from "@/lib/ads/terminal";
 import { clientIpFromHeaders, lookupGeo } from "@/lib/tracker/geo";
 import { parseDevice } from "@/lib/tracker/device";
+import { env } from "@/lib/env";
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
@@ -64,7 +70,11 @@ export async function GET(request: NextRequest) {
   const h = headers(request);
   try {
     const url = new URL(request.url);
-    const slotId = url.searchParams.get("slot");
+    // No ?slot= (someone just curling the bare URL) falls back to the network's
+    // default slot, so the endpoint rotates real campaigns on every load
+    // instead of only ever showing the house ad. Serving needs *a* slot: the
+    // impression row is what a click later resolves back to.
+    const slotId = url.searchParams.get("slot") || env.adsDefaultSlotId;
     const visitorId = url.searchParams.get("v");
     const cols = clampCols(url.searchParams.get("cols") ?? url.searchParams.get("width"));
     const color = wantsColor(url.searchParams.get("color"));
diff --git a/lib/env.ts b/lib/env.ts
index 89fcf527..1a859417 100644
--- a/lib/env.ts
+++ b/lib/env.ts
@@ -15,6 +15,12 @@ export const env = {
     process.env.MAXMIND_GEOLITE2_CITY_DB_PATH ??
     process.env.GEOLITE2_CITY_DB_PATH ??
     "data/GeoLite2-City.mmdb",
+  // Ad network — slot used when a serving request names none (the bare
+  // /api/ads/motd URL). Without it a slotless request can't meter an
+  // impression, so it can only ever return the house ad. Points at the
+  // network's own publisher slot: anonymous terminal traffic is CrawlProof's
+  // own inventory, so its impressions/clicks accrue there.
+  adsDefaultSlotId: process.env.ADS_DEFAULT_SLOT_ID ?? "",
   // CoinPay — crypto credit purchases.
   coinpayMerchantId: process.env.COINPAY_MERCHANT_ID ?? "",
   coinpayApiKey: process.env.COINPAY_API_KEY ?? "",