diff --git a/p/db/journeys-req.js b/p/db/journeys-req.js
index 9b0fa122..c5164a58 100644
--- a/p/db/journeys-req.js
+++ b/p/db/journeys-req.js
@@ -7,7 +7,7 @@ const formatJourneysReq = (ctx, from, to, when, outFrwd, journeysRef) => {
 	// TODO opt.accessibility
 	// TODO routingMode
 	let query = {
-		maxUmstiege: opt.transfers,
+		maxUmstiege: opt.transfers === -1 ? undefined : opt.transfers, // setting `maxUmstiege` to -1 is not allowed, see https://github.com/public-transport/db-vendo-client/issues/5
 		minUmstiegszeit: opt.transferTime,
 		deutschlandTicketVorhanden: false,
 		nurDeutschlandTicketVerbindungen: false,
diff --git a/p/dbnav/journeys-req.js b/p/dbnav/journeys-req.js
index 70216c28..653a6c48 100644
--- a/p/dbnav/journeys-req.js
+++ b/p/dbnav/journeys-req.js
@@ -46,7 +46,7 @@ const formatJourneysReq = (ctx, from, to, when, outFrwd, journeysRef) => {
 				? [{locationId: profile.formatLocation(profile, opt.via, 'opt.via').lid}]
 				: undefined,
 			zielLocationId: to.lid,
-			maxUmstiege: opt.transfers || undefined,
+			maxUmstiege: opt.transfers === -1 ? undefined : opt.transfers, // setting `maxUmstiege` to -1 is not allowed, see https://github.com/public-transport/db-vendo-client/issues/5
 			minUmstiegsdauer: opt.transferTime || undefined,
 			fahrradmitnahme: opt.bike,
 		},