--- a/vehicle.c	Fri Jun 22 20:06:59 2007 +0000
+++ b/vehicle.c	Fri Jun 22 20:08:37 2007 +0000
@@ -36,7 +36,7 @@
 #include "newgrf_engine.h"
 #include "newgrf_sound.h"
 
-#define INVALID_COORD (-0x8000)
+#define INVALID_COORD (0x7fffffff)
 #define GEN_HASH(x, y) ((GB((y), 6, 6) << 6) + GB((x), 7, 6))
 
 /*
@@ -823,17 +823,29 @@
 	const int b = dpi->top + dpi->height;
 
 	// The hash area to scan
-	const int xl = GB(l - 70, 7, 6);
-	const int xu = GB(r,      7, 6);
-	const int yl = GB(t - 70, 6, 6) << 6;
-	const int yu = GB(b,      6, 6) << 6;
-
-	int x;
-	int y;
+	int xl, xu, yl, yu, x, y;
+
+	if (dpi->width + 70 < (1 << (7 + 6))) {
+		xl = GB(l - 70, 7, 6);
+		xu = GB(r,      7, 6);
+	} else {
+		/* scan whole hash row */
+		xl = 0;
+		xu = 0x3F;
+	}
+
+	if (dpi->height + 70 < (1 << (6 + 6))) {
+		yl = GB(t - 70, 6, 6) << 6;
+		yu = GB(b,      6, 6) << 6;
+	} else {
+		/* scan whole column */
+		yl = 0;
+		yu = 0x3F << 6;
+	}
 
 	for (y = yl;; y = (y + (1 << 6)) & (0x3F << 6)) {
 		for (x = xl;; x = (x + 1) & 0x3F) {
-			VehicleID veh = _vehicle_position_hash[(x + y) & 0xFFFF];
+			VehicleID veh = _vehicle_position_hash[x + y]; // already masked & 0xFFF
 
 			while (veh != INVALID_VEHICLE) {
 				const Vehicle* v = GetVehicle(veh);