diff --git a/lib/idea-code-server.ts b/lib/idea-code-server.ts
index 9f26aed..819d4ed 100644
--- a/lib/idea-code-server.ts
+++ b/lib/idea-code-server.ts
@@ -7,6 +7,11 @@
 // Geen aparte $transaction nodig voor enkelvoudige update — de update is
 // atomisch op één rij. Voor combineren met een idea.create wordt
 // nextIdeaCode aangeroepen binnen de bredere $transaction van de caller.
+//
+// Self-correcting: na de increment wordt de numerieke MAX van bestaande codes
+// opgevraagd via raw SQL (geen string-vergelijking — die faalt boven IDEA-999).
+// Als de counter achterloopt (bijv. na directe DB-inserts tijdens development)
+// wordt nextN = MAX+1 gebruikt en de counter direct bijgewerkt.
 
 import { prisma } from '@/lib/prisma'
 import { formatIdeaCode } from '@/lib/idea-code'
@@ -17,10 +22,34 @@ export async function nextIdeaCode(
   userId: string,
   client: Prisma.TransactionClient | typeof prisma = prisma,
 ): Promise<string> {
+  // Increment counter — acquires Postgres row lock, serializes concurrent calls.
   const u = await client.user.update({
     where: { id: userId },
     data: { idea_code_counter: { increment: 1 } },
     select: { idea_code_counter: true },
   })
-  return formatIdeaCode(u.idea_code_counter)
+
+  // Numeric MAX guards against counter drift (e.g. ideas inserted directly in
+  // DB without updating the counter). String MAX mis-sorts "IDEA-1000" <
+  // "IDEA-999", so we cast to INTEGER in SQL.
+  const rows = await (client as Prisma.TransactionClient).$queryRaw<
+    [{ max_n: number | bigint | null }]
+  >`
+    SELECT MAX(CAST(SUBSTRING(code FROM 6) AS INTEGER)) AS max_n
+    FROM ideas
+    WHERE user_id = ${userId}
+  `
+  const maxExisting = rows[0].max_n !== null ? Number(rows[0].max_n) : 0
+  const nextN = Math.max(u.idea_code_counter, maxExisting + 1)
+
+  // Re-sync counter forward if it was behind the actual max.
+  if (nextN !== u.idea_code_counter) {
+    await client.user.update({
+      where: { id: userId },
+      data: { idea_code_counter: nextN },
+      select: { id: true },
+    })
+  }
+
+  return formatIdeaCode(nextN)
 }