--- a/src/ai/api/ai_cargo.cpp	Tue Apr 15 22:18:11 2008 +0000
+++ b/src/ai/api/ai_cargo.cpp	Tue Apr 15 22:29:00 2008 +0000
@@ -37,6 +37,6 @@
 
 /* static */ int32 AICargo::GetCargoIncome(CargoID cargo_type, uint32 distance, uint32 days_in_transit)
 {
-	if (!IsValidCargo(cargo_type)) return 0;
+	if (!IsValidCargo(cargo_type)) return -1;
 	return ::GetTransportedGoodsIncome(1, distance, days_in_transit, cargo_type);
 }