diff --git a/server/src/routes/admin.ts b/server/src/routes/admin.ts
index ab1430b..d6b52e7 100644
--- a/server/src/routes/admin.ts
+++ b/server/src/routes/admin.ts
@@ -569,6 +569,14 @@ export function registerAdminRoutes(app: FastifyInstance, db: DB) {
 
 function csvCell(v: unknown): string {
   if (v === null || v === undefined) return '';
+  // Numbers (e.g. a negative total_cents from a net-Pfand-refund
+  // transaction) skip both the formula-injection guard and the quote
+  // escaping below — the guard exists for free-text columns that could
+  // contain a formula-injection payload; a real negative number should
+  // stay a real number, not get coerced into text a spreadsheet can no
+  // longer SUM(). Numbers also never contain `,`/`"`/`\n`, so escaping is
+  // moot for them anyway.
+  if (typeof v === 'number') return String(v);
   let s = String(v);
   // Neutralise spreadsheet formula injection: a cell starting with one of
   // these characters is interpreted as a formula by Excel/LibreOffice when