diff --git a/src/engine.cpp b/src/engine.cpp
--- a/src/engine.cpp
+++ b/src/engine.cpp
@@ -497,6 +497,9 @@ void SetCachedEngineCounts()
 	}
 }
 
+/**
+ * Initialise the engine pool with the data from the original vehicles.
+ */
 void SetupEngines()
 {
 	DeleteWindowByClass(WC_ENGINE_PREVIEW);
@@ -506,6 +509,9 @@ void SetupEngines()
 	const EngineIDMapping *end = _engine_mngr.End();
 	uint index = 0;
 	for (const EngineIDMapping *eid = _engine_mngr.Begin(); eid != end; eid++, index++) {
+		/* Assert is safe; there won't be more than 256 original vehicles
+		 * in any case, and we just cleaned the pool. */
+		assert(Engine::CanAllocateItem());
 		const Engine *e = new Engine(eid->type, eid->internal_id);
 		assert(e->index == index);
 	}
diff --git a/src/saveload/afterload.cpp b/src/saveload/afterload.cpp
--- a/src/saveload/afterload.cpp
+++ b/src/saveload/afterload.cpp
@@ -782,11 +782,18 @@ bool AfterLoadGame()
 					case STATION_TRUCK:
 					case STATION_BUS:
 						if (IsSavegameVersionBefore(6)) {
+							/* Before version 5 you could not have more than 250 stations.
+							 * Version 6 adds large maps, so you could only place 253*253
+							 * road stops on a map (no freeform edges) = 64009. So, yes
+							 * someone could in theory create such a full map to trigger
+							 * this assertion, it's safe to assume that's only something
+							 * theoretical and does not happen in normal games. */
+							assert(RoadStop::CanAllocateItem());
+
 							/* From this version on there can be multiple road stops of the
 							 * same type per station. Convert the existing stops to the new
 							 * internal data structure. */
 							RoadStop *rs = new RoadStop(t);
-							if (rs == NULL) error("Too many road stops in savegame");
 
 							RoadStop **head =
 								IsTruckStop(t) ? &st->truck_stops : &st->bus_stops;
@@ -1928,6 +1935,12 @@ bool AfterLoadGame()
 					ObjectType type = GetObjectType(t);
 					int size = type == OBJECT_HQ ? 2 : 1;
 
+					if (!Object::CanAllocateItem()) {
+						/* Nice... you managed to place 64k lighthouses and
+						 * antennae on the map... boohoo. */
+						SlError(STR_ERROR_TOO_MANY_OBJECTS);
+					}
+
 					Object *o = new Object();
 					o->location.tile = t;
 					o->location.w    = size;
@@ -2024,6 +2037,10 @@ bool AfterLoadGame()
 		FOR_ALL_STATIONS(st) {
 			std::list<Vehicle *>::iterator iter;
 			for (iter = st->loading_vehicles.begin(); iter != st->loading_vehicles.end(); ++iter) {
+				/* There are always as many CargoPayments as Vehicles. We need to make the
+				 * assert() in Pool::GetNew() happy by calling CanAllocateItem(). */
+				assert_compile(CargoPaymentPool::MAX_SIZE == VehiclePool::MAX_SIZE);
+				assert(CargoPayment::CanAllocateItem());
 				Vehicle *v = *iter;
 				if (v->cargo_payment == NULL) v->cargo_payment = new CargoPayment(v);
 			}
diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -472,7 +472,7 @@ static void SlNullPointers()
  * @note This function does never return as it throws an exception to
  *       break out of all the saveload code.
  */
-static void NORETURN SlError(StringID string, const char *extra_msg = NULL)
+void NORETURN SlError(StringID string, const char *extra_msg)
 {
 	/* Distinguish between loading into _load_check_data vs. normal save/load. */
 	if (_sl.action == SLA_LOAD_CHECK) {
diff --git a/src/saveload/saveload.h b/src/saveload/saveload.h
--- a/src/saveload/saveload.h
+++ b/src/saveload/saveload.h
@@ -13,6 +13,7 @@
 #define SAVELOAD_H
 
 #include "../fileio_type.h"
+#include "../strings_type.h"
 
 #ifdef SIZE_MAX
 #undef SIZE_MAX
@@ -539,6 +540,7 @@ void SlGlobList(const SaveLoadGlobVarLis
 void SlArray(void *array, size_t length, VarType conv);
 void SlObject(void *object, const SaveLoad *sld);
 bool SlObjectMember(void *object, const SaveLoad *sld);
+void NORETURN SlError(StringID string, const char *extra_msg = NULL);
 void NORETURN SlErrorCorrupt(const char *msg);
 
 bool SaveloadCrashWithMissingNewGRFs();
diff --git a/src/saveload/station_sl.cpp b/src/saveload/station_sl.cpp
--- a/src/saveload/station_sl.cpp
+++ b/src/saveload/station_sl.cpp
@@ -284,7 +284,11 @@ static void Load_STNS()
 					/* In old versions, enroute_from used 0xFF as INVALID_STATION */
 					StationID source = (IsSavegameVersionBefore(7) && _cargo_source == 0xFF) ? INVALID_STATION : _cargo_source;
 
-					/* Don't construct the packet with station here, because that'll fail with old savegames */
+					/* Make sure we can allocate the CargoPacket. This is safe
+					 * as there can only be ~64k stations and 32 cargos in these
+					 * savegame versions. As the CargoPacketPool has more than
+					 * 16 million entries; it fits by an order of magnitude. */
+					assert(CargoPacket::CanAllocateItem());
 					ge->cargo.Append(new CargoPacket(GB(_waiting_acceptance, 0, 12), _cargo_days, source, _cargo_source_xy, _cargo_source_xy, _cargo_feeder_share));
 					SB(ge->acceptance_pickup, GoodsEntry::PICKUP, 1, 1);
 				}
diff --git a/src/saveload/vehicle_sl.cpp b/src/saveload/vehicle_sl.cpp
--- a/src/saveload/vehicle_sl.cpp
+++ b/src/saveload/vehicle_sl.cpp
@@ -270,6 +270,11 @@ void AfterLoadVehicles(bool part_of_load
 				if (IsSavegameVersionBefore(105)) { // Pre-105 didn't save an OrderList
 					if (mapping[v->orders.old] == NULL) {
 						/* This adds the whole shared vehicle chain for case b */
+
+						/* Creating an OrderList here is safe because the number of vehicles
+						 * allowed in these savegames matches the number of OrderLists. As
+						 * such each vehicle can get an OrderList and it will (still) fit. */
+						assert(OrderList::CanAllocateItem());
 						v->orders.list = mapping[v->orders.old] = new OrderList(v->orders.old, v);
 					} else {
 						v->orders.list = mapping[v->orders.old];
@@ -752,7 +757,7 @@ void Load_VEHS()
 
 		SlObject(v, GetVehicleDescription(vtype));
 
-		if (_cargo_count != 0 && IsCompanyBuildableVehicleType(v)) {
+		if (_cargo_count != 0 && IsCompanyBuildableVehicleType(v) && CargoPacket::CanAllocateItem()) {
 			/* Don't construct the packet with station here, because that'll fail with old savegames */
 			CargoPacket *cp = new CargoPacket(_cargo_count, _cargo_days, _cargo_source, _cargo_source_xy, _cargo_loaded_at_xy, _cargo_feeder_share);
 			v->cargo.Append(cp);