diff --git a/src/engine.cpp b/src/engine.cpp
index b331ddb7f84..e1220f2b7e3 100644
--- a/src/engine.cpp
+++ b/src/engine.cpp
@@ -579,6 +579,7 @@ void EngineOverrideManager::ResetToDefaultMapping()
 			eid.substitute_id   = internal_id;
 		}
 	}
+	this->ReIndex();
 }
 
 /**
@@ -592,14 +593,21 @@ void EngineOverrideManager::ResetToDefaultMapping()
  */
 EngineID EngineOverrideManager::GetID(VehicleType type, uint16_t grf_local_id, uint32_t grfid)
 {
+	auto iter = this->mapping_index.find(HashKey(type, grf_local_id, grfid));
+	EngineID id = (iter != this->mapping_index.end()) ? iter->second : INVALID_ENGINE;
+
+#ifdef _DEBUG
 	EngineID index = 0;
 	for (const EngineIDMapping &eid : *this) {
 		if (eid.type == type && eid.grfid == grfid && eid.internal_id == grf_local_id) {
+			assert(id == index);
 			return index;
 		}
 		index++;
 	}
-	return INVALID_ENGINE;
+	assert(id == INVALID_ENGINE);
+#endif
+	return id;
 }
 
 /**
@@ -620,6 +628,26 @@ bool EngineOverrideManager::ResetToCurrentNewGRFConfig()
 	return true;
 }
 
+void EngineOverrideManager::AddToIndex(EngineID id)
+{
+	this->mapping_index.insert({ HashKey((*this)[id]), id });
+}
+
+void EngineOverrideManager::RemoveFromIndex(EngineID id)
+{
+	this->mapping_index.erase(HashKey((*this)[id]));
+}
+
+void EngineOverrideManager::ReIndex()
+{
+	this->mapping_index.clear();
+	EngineID index = 0;
+	for (const EngineIDMapping &eid : *this) {
+		this->mapping_index.insert({ HashKey(eid), index });
+		index++;
+	}
+}
+
 /**
  * Initialise the engine pool with the data from the original vehicles.
  */
diff --git a/src/engine_override.h b/src/engine_override.h
index 8e6822a796a..fe7872783a3 100644
--- a/src/engine_override.h
+++ b/src/engine_override.h
@@ -13,6 +13,7 @@
 #include "engine_type.h"
 #include "vehicle_type.h"
 
+#include "3rdparty/robin_hood/robin_hood.h"
 #include <vector>
 
 struct EngineIDMapping {
@@ -29,9 +30,27 @@ struct EngineIDMapping {
 struct EngineOverrideManager : std::vector<EngineIDMapping> {
 	static const uint NUM_DEFAULT_ENGINES; ///< Number of default entries
 
+private:
+	static uint64_t HashKey(VehicleType type, uint16_t grf_local_id, uint32_t grfid)
+	{
+		return grfid | (static_cast<uint64_t>(grf_local_id) << 32) | (static_cast<uint64_t>(type) << 48);
+	}
+
+	static uint64_t HashKey(const EngineIDMapping &eid)
+	{
+		return HashKey(eid.type, eid.internal_id, eid.grfid);
+	}
+
+	robin_hood::unordered_map<uint64_t, EngineID> mapping_index;
+
+public:
 	void ResetToDefaultMapping();
 	EngineID GetID(VehicleType type, uint16_t grf_local_id, uint32_t grfid);
 
+	void AddToIndex(EngineID id);
+	void RemoveFromIndex(EngineID id);
+	void ReIndex();
+
 	static bool ResetToCurrentNewGRFConfig();
 };
 
diff --git a/src/newgrf.cpp b/src/newgrf.cpp
index dffab5a9c97..34d70c5411e 100644
--- a/src/newgrf.cpp
+++ b/src/newgrf.cpp
@@ -569,8 +569,10 @@ static Engine *GetNewEngine(const GRFFile *file, VehicleType type, uint16_t inte
 
 		/* Reserve the engine slot */
 		if (!static_access) {
+			_engine_mngr.RemoveFromIndex(engine);
 			EngineIDMapping *eid = _engine_mngr.data() + engine;
 			eid->grfid           = scope_grfid; // Note: this is INVALID_GRFID if dynamic_engines is disabled, so no reservation
+			_engine_mngr.AddToIndex(engine);
 		}
 
 		return e;
@@ -597,6 +599,7 @@ static Engine *GetNewEngine(const GRFFile *file, VehicleType type, uint16_t inte
 			type,
 			std::min<uint8_t>(internal_id, _engine_counts[type]) // substitute_id == _engine_counts[subtype] means "no substitute"
 	});
+	_engine_mngr.AddToIndex(e->index);
 
 	if (engine_pool_size != Engine::GetPoolSize()) {
 		/* Resize temporary engine data ... */
diff --git a/src/saveload/engine_sl.cpp b/src/saveload/engine_sl.cpp
index cde7bd55759..99536a0ee11 100644
--- a/src/saveload/engine_sl.cpp
+++ b/src/saveload/engine_sl.cpp
@@ -115,6 +115,8 @@ struct EIDSChunkHandler : ChunkHandler {
 			EngineIDMapping *eid = &_engine_mngr.emplace_back();
 			SlObject(eid, slt);
 		}
+
+		_engine_mngr.ReIndex();
 	}
 };