diff --git a/src/vehicle_cmd.cpp b/src/vehicle_cmd.cpp
--- a/src/vehicle_cmd.cpp
+++ b/src/vehicle_cmd.cpp
@@ -397,20 +397,16 @@ static CommandCost RefitVehicle(Vehicle 
 		/* Store the result */
 		for (RefitResult *result = refit_result.Begin(); result != refit_result.End(); result++) {
 			Vehicle *u = result->v;
-			if (u->cargo_type != new_cid) {
-				u->cargo.Truncate(u->cargo_cap);
-			} else if (u->cargo_cap > result->capacity) {
-				u->cargo.Truncate(u->cargo_cap - result->capacity);
-			}
+			u->refit_cap = (u->cargo_type == new_cid) ? min(result->capacity, u->refit_cap) : 0;
+			if (u->cargo.TotalCount() > u->refit_cap) u->cargo.Truncate(u->cargo.TotalCount() - u->refit_cap);
 			u->cargo_type = new_cid;
 			u->cargo_cap = result->capacity;
 			u->cargo_subtype = result->subtype;
 			if (u->type == VEH_AIRCRAFT) {
 				Vehicle *w = u->Next();
-				if (w->cargo_cap > result->mail_capacity) {
-					w->cargo.Truncate(w->cargo_cap - result->mail_capacity);
-				}
+				w->refit_cap = min(w->refit_cap, result->mail_capacity);
 				w->cargo_cap = result->mail_capacity;
+				if (w->cargo.TotalCount() > w->refit_cap) w->cargo.Truncate(w->cargo.TotalCount() - w->refit_cap);
 			}
 		}
 	}