diff --git a/src/lib/billing.ts b/src/lib/billing.ts
index 3a6e940..60762e4 100644
--- a/src/lib/billing.ts
+++ b/src/lib/billing.ts
@@ -1411,7 +1411,19 @@ export async function issueCustomInvoiceDraft(params: {
 
   let pdfBuffer: Buffer | null = null;
   try {
-    pdfBuffer = await renderInvoicePdf(placeholder, invoiceDraft.lines);
+    pdfBuffer = await renderInvoicePdf(
+      placeholder,
+      // Same pattern as the auto-cron generateInvoice: synthesize
+      // temporary ids for the PDF renderer. The real DB rows have
+      // these populated post-insert, but the renderer only reads
+      // them for React keys (display) and id-comparison-free
+      // operations, so synthetic values are fine.
+      invoiceDraft.lines.map((l, i) => ({
+        ...l,
+        id: `tmp-${i}`,
+        invoiceId: placeholder.id,
+      }))
+    );
     const filename = `${placeholder.invoiceNumber}.pdf`;
     await updateInvoicePdf(placeholder.id, pdfBuffer, filename);
   } catch (e) {
@@ -1518,5 +1530,12 @@ export async function renderCustomDraftPreview(
     refundedTotalChf: 0,
     createdAt: new Date().toISOString(),
   };
-  return renderInvoicePdf(fakeInvoice, invoiceDraft.lines);
+  return renderInvoicePdf(
+    fakeInvoice,
+    invoiceDraft.lines.map((l, i) => ({
+      ...l,
+      id: `tmp-${i}`,
+      invoiceId: fakeInvoice.id,
+    }))
+  );
 }