diff --git a/format/transfers.js b/format/transfers.js
index c374a7dd..239e617b 100644
--- a/format/transfers.js
+++ b/format/transfers.js
@@ -1,5 +1,5 @@
 const formatTransfers = (transfers) => {
-	if (transfers === -1) { // profiles may not accept -1: https://github.com/public-transport/db-vendo-client/issues/5
+	if (transfers === null || transfers === -1) { // profiles may not accept -1: https://github.com/public-transport/db-vendo-client/issues/5
 		return undefined;
 	}
 	return transfers;