diff --git a/lib/__tests__/resolve-page-id.test.ts b/lib/__tests__/resolve-page-id.test.ts
index a056583fdb..3fd1223025 100644
--- a/lib/__tests__/resolve-page-id.test.ts
+++ b/lib/__tests__/resolve-page-id.test.ts
@@ -1,6 +1,10 @@
 import { describe, expect, it } from 'vitest'
 
-import { lookupSlug, resolvePageIdFromMaps } from '../resolve-page-id'
+import {
+  isResolvablePageSlug,
+  lookupSlug,
+  resolvePageIdFromMaps
+} from '../resolve-page-id'
 
 const maps = {
   pageUrlOverrides: {
@@ -50,3 +54,23 @@ describe('lookupSlug', () => {
     ).toBe('2bc5cb08-cf2c-810b-83af-c01fde10aefa')
   })
 })
+
+describe('isResolvablePageSlug', () => {
+  it('accepts slugs in the committed index', () => {
+    expect(isResolvablePageSlug('oct-25', maps)).toBe(true)
+  })
+
+  it('accepts slugs from override-page collections', () => {
+    expect(
+      isResolvablePageSlug('rapid-prototyping-highlighty', maps, {
+        'rapid-prototyping-highlighty': '2bc5cb08-cf2c-810b-83af-c01fde10aefa'
+      })
+    ).toBe(true)
+  })
+
+  it('rejects leftover posts that are not on any public listing', () => {
+    expect(
+      isResolvablePageSlug('rapid-prototyping-highlighty-part-2', maps)
+    ).toBe(false)
+  })
+})
diff --git a/lib/resolve-page-id.ts b/lib/resolve-page-id.ts
index d6dc425d12..36b0038be6 100644
--- a/lib/resolve-page-id.ts
+++ b/lib/resolve-page-id.ts
@@ -47,3 +47,18 @@ export function lookupSlug(
   const pageId = slugMap[slug] || slugMap[normalized]
   return pageId ? (parsePageId(pageId) ?? undefined) : undefined
 }
+
+/**
+ * True when `/<slug>` would resolve the same way `resolveNotionPage` does:
+ * committed index / URL overrides, then collection slugs from override pages.
+ * Used to keep the RSS feed from advertising leftover posts that 404.
+ */
+export function isResolvablePageSlug(
+  slug: string,
+  maps: PageIdLookupMaps,
+  extraSlugMap: Record<string, string> = {}
+): boolean {
+  return Boolean(
+    resolvePageIdFromMaps(slug, maps) || lookupSlug(slug, extraSlugMap)
+  )
+}
diff --git a/pages/feed.tsx b/pages/feed.tsx
index a654c8096f..4f67485725 100644
--- a/pages/feed.tsx
+++ b/pages/feed.tsx
@@ -12,8 +12,13 @@ import RSS from 'rss'
 import * as config from '@/lib/config'
 import { getSocialImageUrl } from '@/lib/get-social-image-url'
 import { notion } from '@/lib/notion-api'
+import { canonicalPageMap } from '@/lib/notion-index'
 import { getPageSlug } from '@/lib/page-slug'
-import { getCollectionBlockIds } from '@/lib/posts-collection'
+import {
+  getCollectionBlockIds,
+  getOverrideCollectionSlugMap
+} from '@/lib/posts-collection'
+import { isResolvablePageSlug } from '@/lib/resolve-page-id'
 
 export const getServerSideProps: GetServerSideProps = async ({ req, res }) => {
   if (req.method !== 'GET') {
@@ -94,6 +99,13 @@ export const getServerSideProps: GetServerSideProps = async ({ req, res }) => {
       return { props: {} }
     }
 
+    const extraSlugMap = await getOverrideCollectionSlugMap()
+    const pageIdMaps = {
+      pageUrlOverrides: config.pageUrlOverrides,
+      pageUrlAdditions: config.pageUrlAdditions,
+      canonicalPageMap
+    }
+
     // Get all pages that belong to this collection
     for (const blockId of collectionBlockIds) {
       const block =
@@ -124,6 +136,10 @@ export const getServerSideProps: GetServerSideProps = async ({ req, res }) => {
         config.description
 
       const slug = getPageSlug(block, recordMap) || pageId
+      if (!isResolvablePageSlug(slug, pageIdMaps, extraSlugMap)) {
+        console.warn('skipping feed item with unresolvable slug', slug)
+        continue
+      }
       const url = `${config.host}/${slug}`
 
       const lastUpdatedTime = getPageProperty<number>(