diff --git a/public/invoice-view.js b/public/invoice-view.js
index 5adbba0..3095ba8 100644
--- a/public/invoice-view.js
+++ b/public/invoice-view.js
@@ -245,7 +245,7 @@ function renderInvoiceRow(invoice) {
 
     // Mark Sent button (right side) — only when open, not paid/partial
     let sendBtn = '';
-    if (hasQbo && !paid && !partial && invoice.email_status !== 'sent') {
+    if (hasQbo && !paid && !partial && !overdue && invoice.email_status !== 'sent') {
         sendBtn = `<button onclick="window.invoiceView.setEmailStatus(${invoice.id}, 'sent')" class="text-indigo-600 hover:text-indigo-800 text-xs font-medium" title="Mark as sent to customer">📤 Mark Sent</button>`;
     }