diff --git a/src/routes/admin/dashboard.ts b/src/routes/admin/dashboard.ts
index 8a9c525..f88dc88 100644
--- a/src/routes/admin/dashboard.ts
+++ b/src/routes/admin/dashboard.ts
@@ -179,6 +179,11 @@ export default async function dashboardRoutes(
 
     // Invoices — only for invoices.view
     if (has("invoices.view")) {
+      // $queryRaw template literal interpolation with Date objects fails on
+      // MySQL when Date.toJSON is overridden — pass strings instead.
+      const monthStartStr = monthStart.toJSON();
+      const monthEndStr = monthEnd.toJSON();
+
       const [unpaidCount, revenueAgg] = await Promise.all([
         prisma.invoices.count({ where: { status: "issued" } }),
         prisma.$queryRaw<
@@ -187,7 +192,7 @@ export default async function dashboardRoutes(
           SELECT i.currency, SUM(ii.quantity * ii.unit_price) as total
           FROM invoices i
           JOIN invoice_items ii ON i.id = ii.invoice_id
-          WHERE i.issue_date >= ${monthStart} AND i.issue_date < ${monthEnd}
+          WHERE i.issue_date >= ${monthStartStr} AND i.issue_date < ${monthEndStr}
           GROUP BY i.currency
         `,
       ]);