diff --git a/src/newgrf.cpp b/src/newgrf.cpp
index bd283fa6d8..108eef1c96 100644
--- a/src/newgrf.cpp
+++ b/src/newgrf.cpp
@@ -5781,7 +5781,7 @@ static void TownHouseMapSpriteGroup(ByteReader *buf, uint8 idcount)
 	if (!IsValidGroupID(groupid, "TownHouseMapSpriteGroup")) return;
 
 	for (uint i = 0; i < idcount; i++) {
-		HouseSpec *hs = _cur.grffile->housespec[houses[i]];
+		HouseSpec *hs = houses[i] >= NUM_HOUSES_PER_GRF ? nullptr : _cur.grffile->housespec[houses[i]];
 
 		if (hs == nullptr) {
 			grfmsg(1, "TownHouseMapSpriteGroup: House %d undefined, skipping.", houses[i]);