diff --git a/src/base_station_base.h b/src/base_station_base.h
index 6d72322b85..03a5583943 100644
--- a/src/base_station_base.h
+++ b/src/base_station_base.h
@@ -22,13 +22,13 @@ extern StationPool _station_pool;
 struct StationSpecList {
 	const StationSpec *spec;
 	uint32 grfid;      ///< GRF ID of this custom station
-	uint8  localidx;   ///< Station ID within GRF of station
+	uint16_t localidx; ///< Station ID within GRF of station
 };
 
 struct RoadStopSpecList {
 	const RoadStopSpec *spec;
 	uint32 grfid;      ///< GRF ID of this custom road stop
-	uint8  localidx;   ///< Station ID within GRF of road stop
+	uint16_t localidx; ///< Station ID within GRF of road stop
 };
 
 struct RoadStopTileData {
diff --git a/src/newgrf_class.h b/src/newgrf_class.h
index a0073d1dd4..8946f84350 100644
--- a/src/newgrf_class.h
+++ b/src/newgrf_class.h
@@ -61,7 +61,7 @@ public:
 	static Tid GetUIClass(uint index);
 	static NewGRFClass *Get(Tid cls_id);
 
-	static const Tspec *GetByGrf(uint32 grfid, byte local_id, int *index);
+	static const Tspec *GetByGrf(uint32 grfid, uint16_t local_id, int *index);
 };
 
 #endif /* NEWGRF_CLASS_H */
diff --git a/src/newgrf_class_func.h b/src/newgrf_class_func.h
index 107ab83a36..8b09a5dfa4 100644
--- a/src/newgrf_class_func.h
+++ b/src/newgrf_class_func.h
@@ -187,7 +187,7 @@ DEFINE_NEWGRF_CLASS_METHOD(int)::GetUIFromIndex(int index) const
  * @param index    Pointer to return the index of the spec in its class. If nullptr then not used.
  * @return The spec.
  */
-DEFINE_NEWGRF_CLASS_METHOD(const Tspec *)::GetByGrf(uint32 grfid, byte local_id, int *index)
+DEFINE_NEWGRF_CLASS_METHOD(const Tspec *)::GetByGrf(uint32 grfid, uint16_t local_id, int *index)
 {
 	uint j;
 
@@ -222,4 +222,4 @@ DEFINE_NEWGRF_CLASS_METHOD(const Tspec *)::GetByGrf(uint32 grfid, byte local_id,
 	template const Tspec *name::GetSpec(uint index) const; \
 	template int name::GetUIFromIndex(int index) const; \
 	template int name::GetIndexFromUI(int ui_index) const; \
-	template const Tspec *name::GetByGrf(uint32 grfid, byte localidx, int *index);
+	template const Tspec *name::GetByGrf(uint32 grfid, uint16_t local_id, int *index);
diff --git a/src/newgrf_commons.cpp b/src/newgrf_commons.cpp
index c33c80beec..a44d4662e2 100644
--- a/src/newgrf_commons.cpp
+++ b/src/newgrf_commons.cpp
@@ -58,7 +58,7 @@ OverrideManagerBase::OverrideManagerBase(uint16 offset, uint16 maximum, uint16 i
  * @param grfid  ID of the grf file
  * @param entity_type original entity type
  */
-void OverrideManagerBase::Add(uint8 local_id, uint32 grfid, uint entity_type)
+void OverrideManagerBase::Add(uint16_t local_id, uint32 grfid, uint entity_type)
 {
 	assert(entity_type < this->max_offset);
 	/* An override can be set only once */
@@ -86,7 +86,7 @@ void OverrideManagerBase::ResetOverride()
  * @param grfid ID of the grf file
  * @return the ID of the candidate, of the Invalid flag item ID
  */
-uint16 OverrideManagerBase::GetID(uint8 grf_local_id, uint32 grfid) const
+uint16 OverrideManagerBase::GetID(uint16_t grf_local_id, uint32 grfid) const
 {
 	for (uint16 id = 0; id < this->max_entities; id++) {
 		const EntityIDMapping *map = &this->mappings[id];
@@ -105,7 +105,7 @@ uint16 OverrideManagerBase::GetID(uint8 grf_local_id, uint32 grfid) const
  * @param substitute_id is the original entity from which data is copied for the new one
  * @return the proper usable slot id, or invalid marker if none is found
  */
-uint16 OverrideManagerBase::AddEntityID(byte grf_local_id, uint32 grfid, byte substitute_id)
+uint16 OverrideManagerBase::AddEntityID(uint16_t grf_local_id, uint32 grfid, uint16_t substitute_id)
 {
 	uint16 id = this->GetID(grf_local_id, grfid);
 
@@ -184,7 +184,7 @@ void HouseOverrideManager::SetEntitySpec(const HouseSpec *hs)
  * @param grfid ID of the grf file
  * @return the ID of the candidate, of the Invalid flag item ID
  */
-uint16 IndustryOverrideManager::GetID(uint8 grf_local_id, uint32 grfid) const
+uint16 IndustryOverrideManager::GetID(uint16_t grf_local_id, uint32 grfid) const
 {
 	uint16 id = OverrideManagerBase::GetID(grf_local_id, grfid);
 	if (id != this->invalid_id) return id;
@@ -204,7 +204,7 @@ uint16 IndustryOverrideManager::GetID(uint8 grf_local_id, uint32 grfid) const
  * @param substitute_id industry from which data has been copied
  * @return a free entity id (slotid) if ever one has been found, or Invalid_ID marker otherwise
  */
-uint16 IndustryOverrideManager::AddEntityID(byte grf_local_id, uint32 grfid, byte substitute_id)
+uint16 IndustryOverrideManager::AddEntityID(uint16_t grf_local_id, uint32 grfid, uint16 substitute_id)
 {
 	/* This entity hasn't been defined before, so give it an ID now. */
 	for (uint16 id = 0; id < this->max_entities; id++) {
diff --git a/src/newgrf_commons.h b/src/newgrf_commons.h
index a53752ed0e..06e5fb5f7c 100644
--- a/src/newgrf_commons.h
+++ b/src/newgrf_commons.h
@@ -185,8 +185,8 @@ private:
  */
 struct EntityIDMapping {
 	uint32 grfid;          ///< The GRF ID of the file the entity belongs to
-	uint8  entity_id;      ///< The entity ID within the GRF file
-	uint8  substitute_id;  ///< The (original) entity ID to use if this GRF is not available
+	uint16_t entity_id; ///< The entity ID within the GRF file
+	uint16_t substitute_id; ///< The (original) entity ID to use if this GRF is not available
 };
 
 class OverrideManagerBase {
@@ -209,12 +209,12 @@ public:
 	void ResetOverride();
 	void ResetMapping();
 
-	void Add(uint8 local_id, uint32 grfid, uint entity_type);
-	virtual uint16 AddEntityID(byte grf_local_id, uint32 grfid, byte substitute_id);
+	void Add(uint16_t local_id, uint32 grfid, uint entity_type);
+	virtual uint16 AddEntityID(uint16_t grf_local_id, uint32 grfid, uint16_t substitute_id);
 
 	uint32 GetGRFID(uint16 entity_id) const;
 	uint16 GetSubstituteID(uint16 entity_id) const;
-	virtual uint16 GetID(uint8 grf_local_id, uint32 grfid) const;
+	virtual uint16 GetID(uint16_t grf_local_id, uint32 grfid) const;
 
 	inline uint16 GetMaxMapping() const { return this->max_entities; }
 	inline uint16 GetMaxOffset() const { return this->max_offset; }
@@ -237,8 +237,8 @@ public:
 	IndustryOverrideManager(uint16 offset, uint16 maximum, uint16 invalid) :
 			OverrideManagerBase(offset, maximum, invalid) {}
 
-	uint16 AddEntityID(byte grf_local_id, uint32 grfid, byte substitute_id) override;
-	uint16 GetID(uint8 grf_local_id, uint32 grfid) const override;
+	uint16 AddEntityID(uint16_t grf_local_id, uint32 grfid, uint16_t substitute_id) override;
+	uint16 GetID(uint16_t grf_local_id, uint32 grfid) const override;
 
 	void SetEntitySpec(IndustrySpec *inds);
 };
diff --git a/src/newgrf_roadstop.cpp b/src/newgrf_roadstop.cpp
index a311ee2f79..d59457d94b 100644
--- a/src/newgrf_roadstop.cpp
+++ b/src/newgrf_roadstop.cpp
@@ -157,7 +157,7 @@ uint32 RoadStopScopeResolver::GetVariable(byte variable, uint32 parameter, bool
 
 			if (IsCustomRoadStopSpecIndex(nearby_tile)) {
 				const RoadStopSpecList ssl = BaseStation::GetByTile(nearby_tile)->roadstop_speclist[GetCustomRoadStopSpecIndex(nearby_tile)];
-				res |= 1 << (ssl.grfid != grfid ? 9 : 8) | ssl.localidx;
+				res |= 1 << (ssl.grfid != grfid ? 9 : 8) | std::max<uint16_t>(ssl.localidx, 0xFF);
 			}
 			return res;
 		}
diff --git a/src/newgrf_station.cpp b/src/newgrf_station.cpp
index ba6ee47fad..b40674250b 100644
--- a/src/newgrf_station.cpp
+++ b/src/newgrf_station.cpp
@@ -364,7 +364,7 @@ TownScopeResolver *StationResolverObject::GetTown()
 
 			if (IsCustomStationSpecIndex(nearby_tile)) {
 				const StationSpecList ssl = BaseStation::GetByTile(nearby_tile)->speclist[GetCustomStationSpecIndex(nearby_tile)];
-				res |= 1 << (ssl.grfid != grfid ? 9 : 8) | ssl.localidx;
+				res |= 1 << (ssl.grfid != grfid ? 9 : 8) | std::max<uint16_t>(ssl.localidx, 0xFF);
 			}
 			return res;
 		}
diff --git a/src/saveload/newgrf_sl.cpp b/src/saveload/newgrf_sl.cpp
index d15057564a..1c2fd7ff24 100644
--- a/src/saveload/newgrf_sl.cpp
+++ b/src/saveload/newgrf_sl.cpp
@@ -20,8 +20,10 @@
 /** Save and load the mapping between a spec and the NewGRF it came from. */
 static const SaveLoad _newgrf_mapping_desc[] = {
 	SLE_VAR(EntityIDMapping, grfid,         SLE_UINT32),
-	SLE_VAR(EntityIDMapping, entity_id,     SLE_UINT8),
-	SLE_VAR(EntityIDMapping, substitute_id, SLE_UINT8),
+	SLE_CONDVAR(EntityIDMapping, entity_id,     SLE_FILE_U8 | SLE_VAR_U16, SL_MIN_VERSION,            SLV_EXTEND_ENTITY_MAPPING),
+	SLE_CONDVAR(EntityIDMapping, entity_id,     SLE_UINT16,                SLV_EXTEND_ENTITY_MAPPING, SL_MAX_VERSION),
+	SLE_CONDVAR(EntityIDMapping, substitute_id, SLE_FILE_U8 | SLE_VAR_U16, SL_MIN_VERSION,            SLV_EXTEND_ENTITY_MAPPING),
+	SLE_CONDVAR(EntityIDMapping, substitute_id, SLE_UINT16,                SLV_EXTEND_ENTITY_MAPPING, SL_MAX_VERSION),
 };
 
 /**
diff --git a/src/saveload/saveload.h b/src/saveload/saveload.h
index f95ec57150..a00171abd7 100644
--- a/src/saveload/saveload.h
+++ b/src/saveload/saveload.h
@@ -354,6 +354,7 @@ enum SaveLoadVersion : uint16 {
 	SLV_AI_START_DATE,                      ///< 309  PR#10653 Removal of individual AI start dates and added a generic one.
 
 	SLV_EXTEND_VEHICLE_RANDOM,              ///< 310  PR#10701 Extend vehicle random bits.
+	SLV_EXTEND_ENTITY_MAPPING,              ///< 311  PR#10672 Extend entity mapping range.
 
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 };
diff --git a/src/saveload/station_sl.cpp b/src/saveload/station_sl.cpp
index 277bf9652b..93f4db3171 100644
--- a/src/saveload/station_sl.cpp
+++ b/src/saveload/station_sl.cpp
@@ -205,8 +205,9 @@ static void SwapPackets(GoodsEntry *ge)
 class SlStationSpecList : public DefaultSaveLoadHandler<SlStationSpecList, BaseStation> {
 public:
 	inline static const SaveLoad description[] = {
-		SLE_CONDVAR(StationSpecList, grfid,    SLE_UINT32, SLV_27, SL_MAX_VERSION),
-		SLE_CONDVAR(StationSpecList, localidx, SLE_UINT8,  SLV_27, SL_MAX_VERSION),
+		SLE_CONDVAR(StationSpecList, grfid,    SLE_UINT32,                SLV_27,                    SL_MAX_VERSION),
+		SLE_CONDVAR(StationSpecList, localidx, SLE_FILE_U8 | SLE_VAR_U16, SLV_27,                    SLV_EXTEND_ENTITY_MAPPING),
+		SLE_CONDVAR(StationSpecList, localidx, SLE_UINT16,                SLV_EXTEND_ENTITY_MAPPING, SL_MAX_VERSION),
 	};
 	inline const static SaveLoadCompatTable compat_description = _station_spec_list_sl_compat;
 
@@ -236,8 +237,9 @@ uint8 SlStationSpecList::last_num_specs;
 class SlRoadStopSpecList : public DefaultSaveLoadHandler<SlRoadStopSpecList, BaseStation> {
 public:
 	inline static const SaveLoad description[] = {
-		SLE_VAR(RoadStopSpecList, grfid,    SLE_UINT32),
-		SLE_VAR(RoadStopSpecList, localidx, SLE_UINT8),
+		    SLE_VAR(RoadStopSpecList, grfid,    SLE_UINT32),
+		SLE_CONDVAR(RoadStopSpecList, localidx, SLE_FILE_U8 | SLE_VAR_U16, SLV_27,                    SLV_EXTEND_ENTITY_MAPPING),
+		SLE_CONDVAR(RoadStopSpecList, localidx, SLE_UINT16,                SLV_EXTEND_ENTITY_MAPPING, SL_MAX_VERSION),
 	};
 	inline const static SaveLoadCompatTable compat_description = _station_road_stop_spec_list_sl_compat;