--- a/vehicle.c	Wed Mar 29 20:41:15 2006 +0000
+++ b/vehicle.c	Wed Mar 29 20:57:17 2006 +0000
@@ -1552,6 +1552,8 @@
 
 			if (v->type != VEH_Road) { // road vehicles can't be refitted
 				if (v->cargo_type != w->cargo_type) {
+					// we can't pay for refitting because we can't estimate refitting costs for a vehicle before it's build
+					// if we pay for it anyway, the cost and the estimated cost will not be the same and we will have an assert
 					DoCommand(x, y, w->index, v->cargo_type, flags, CMD_REFIT_VEH(v->type));
 				}
 			}