diff --git a/actions/ideas.ts b/actions/ideas.ts
index 1ae5e47..dbfa806 100644
--- a/actions/ideas.ts
+++ b/actions/ideas.ts
@@ -10,6 +10,8 @@ import { revalidatePath } from 'next/cache'
 import { cookies } from 'next/headers'
 import { getIronSession } from 'iron-session'
 
+import { z } from 'zod'
+
 import { prisma } from '@/lib/prisma'
 import { SessionData, sessionOptions } from '@/lib/session'
 import { enforceUserRateLimit } from '@/lib/rate-limit'
@@ -165,6 +167,63 @@ export async function deleteIdeaAction(id: string): Promise<ActionResult> {
   return { success: true }
 }
 
+// ---------------------------------------------------------------------------
+// Secondary products
+
+const secondaryProductsSchema = z.object({
+  ideaId: z.string().cuid(),
+  productIds: z.array(z.string().cuid()).max(10),
+})
+
+export async function updateSecondaryProductsAction(
+  ideaId: string,
+  productIds: string[],
+): Promise<ActionResult> {
+  const session = await getSession()
+  if (!session.userId) return { error: 'Niet ingelogd', code: 401 }
+  if (session.isDemo) return { error: 'Niet beschikbaar in demo-modus', code: 403 }
+
+  const parsed = secondaryProductsSchema.safeParse({ ideaId, productIds })
+  if (!parsed.success) return { error: 'Ongeldige invoer', code: 422 }
+
+  const idea = await prisma.idea.findFirst({
+    where: { id: parsed.data.ideaId, user_id: session.userId },
+    select: { id: true, product_id: true },
+  })
+  if (!idea) return { error: 'Idee niet gevonden', code: 404 }
+
+  // Verwijder primair product uit de lijst (mag niet dubbel)
+  const filtered = parsed.data.productIds.filter((pid) => pid !== idea.product_id)
+
+  // Valideer dat alle gevraagde producten toegankelijk zijn voor de user
+  if (filtered.length > 0) {
+    const { productAccessFilter } = await import('@/lib/product-access')
+    const accessible = await prisma.product.findMany({
+      where: { id: { in: filtered }, ...productAccessFilter(session.userId) },
+      select: { id: true },
+    })
+    if (accessible.length !== filtered.length)
+      return { error: 'Een of meer producten zijn niet toegankelijk', code: 403 }
+  }
+
+  // Atomisch: verwijder alle bestaande, voeg nieuwe in
+  await prisma.$transaction([
+    prisma.ideaProduct.deleteMany({ where: { idea_id: idea.id } }),
+    ...(filtered.length > 0
+      ? [
+          prisma.ideaProduct.createMany({
+            data: filtered.map((pid) => ({ idea_id: idea.id, product_id: pid })),
+            skipDuplicates: true,
+          }),
+        ]
+      : []),
+  ])
+
+  revalidatePath('/ideas/' + idea.id, 'page')
+  revalidatePath('/ideas', 'page')
+  return { success: true }
+}
+
 // ---------------------------------------------------------------------------
 // Markdown-edits (grill_md & plan_md handmatig fine-tunen)