diff --git a/include/osm_lua_processing.h b/include/osm_lua_processing.h
index c111c00b..66fe8872 100644
--- a/include/osm_lua_processing.h
+++ b/include/osm_lua_processing.h
@@ -92,7 +92,7 @@ class OsmLuaProcessing {
 	bool Holds(const std::string& key) const;
 
 	// Get an OSM tag for a given key (or return empty string if none)
-	std::string Find(const std::string& key) const;
+	const std::string& Find(const std::string& key) const;
 
 	// ----	Spatial queries called from Lua
 
@@ -249,7 +249,7 @@ class OsmLuaProcessing {
 	class LayerDefinition &layers;
 	
 	std::deque<std::pair<OutputObjectRef, AttributeStoreRef>> outputs;			///< All output objects that have been created
-	boost::container::flat_map<std::string, std::string> currentTags;
+	const boost::container::flat_map<std::string, std::string>* currentTags;
 };
 
 #endif //_OSM_LUA_PROCESSING_H
diff --git a/include/read_pbf.h b/include/read_pbf.h
index 89077a6e..7761dc58 100644
--- a/include/read_pbf.h
+++ b/include/read_pbf.h
@@ -37,6 +37,7 @@ class PbfReader
 	using tag_map_t = boost::container::flat_map<std::string, std::string>;
 	template<typename T>
 	void readTags(T &pbfObject, PrimitiveBlock const &pb, tag_map_t &tags) {
+		tags.reserve(pbfObject.keys_size());
 		auto keysPtr = pbfObject.mutable_keys();
 		auto valsPtr = pbfObject.mutable_vals();
 		for (uint n=0; n < pbfObject.keys_size(); n++) {
diff --git a/src/osm_lua_processing.cpp b/src/osm_lua_processing.cpp
index d368ed8d..0137851d 100644
--- a/src/osm_lua_processing.cpp
+++ b/src/osm_lua_processing.cpp
@@ -7,6 +7,7 @@ using namespace std;
 
 thread_local kaguya::State *g_luaState = nullptr;
 bool supportsRemappingShapefiles = false;
+const std::string EMPTY_STRING = "";
 
 int lua_error_handler(int errCode, const char *errMessage)
 {
@@ -30,6 +31,7 @@ OsmLuaProcessing::OsmLuaProcessing(
 	osmMemTiles(osmMemTiles),
 	attributeStore(attributeStore),
 	config(configIn),
+	currentTags(NULL),
 	layers(layers) {
 
 	// ----	Initialise Lua
@@ -114,13 +116,13 @@ string OsmLuaProcessing::Id() const {
 
 // Check if there's a value for a given key
 bool OsmLuaProcessing::Holds(const string& key) const {
-	return currentTags.find(key) != currentTags.end();
+	return currentTags->find(key) != currentTags->end();
 }
 
 // Get an OSM tag for a given key (or return empty string if none)
-string OsmLuaProcessing::Find(const string& key) const {
-	auto it = currentTags.find(key);
-	if(it == currentTags.end()) return "";
+const string& OsmLuaProcessing::Find(const string& key) const {
+	auto it = currentTags->find(key);
+	if(it == currentTags->end()) return EMPTY_STRING;
 	return it->second;
 }
 
@@ -546,7 +548,7 @@ bool OsmLuaProcessing::scanRelation(WayID id, const tag_map_t &tags) {
 	originalOsmID = id;
 	isWay = false;
 	isRelation = true;
-	currentTags = tags;
+	currentTags = &tags;
 	try {
 		luaState["relation_scan_function"](this);
 	} catch(luaProcessingException &e) {
@@ -568,7 +570,7 @@ void OsmLuaProcessing::setNode(NodeID id, LatpLon node, const tag_map_t &tags) {
 	isRelation = false;
 	lon = node.lon;
 	latp= node.latp;
-	currentTags = tags;
+	currentTags = &tags;
 
 	//Start Lua processing for node
 	try {
@@ -617,7 +619,7 @@ void OsmLuaProcessing::setWay(WayID wayId, LatpLonVec const &llVec, const tag_ma
 		throw std::out_of_range(ss.str());
 	}
 
-	currentTags = tags;
+	currentTags = &tags;
 
 	bool ok = true;
 	if (ok) {
@@ -705,7 +707,7 @@ void OsmLuaProcessing::setRelation(int64_t relationId, WayVec const &outerWayVec
 	llVecPtr = nullptr;
 	outerWayVecPtr = &outerWayVec;
 	innerWayVecPtr = &innerWayVec;
-	currentTags = tags;
+	currentTags = &tags;
 
 	// Start Lua processing for relation
 	if (!isNativeMP && !supportsWritingRelations) return;
diff --git a/src/read_pbf.cpp b/src/read_pbf.cpp
index bd800398..5b1795cb 100644
--- a/src/read_pbf.cpp
+++ b/src/read_pbf.cpp
@@ -44,12 +44,14 @@ bool PbfReader::ReadNodes(OsmLuaProcessing &output, PrimitiveGroup &pg, Primitiv
 				}
 				kvPos++;
 			}
-			// For tagged nodes, call Lua, then save the OutputObject
-			boost::container::flat_map<std::string, std::string> tags;
 
 			nodes.push_back(std::make_pair(static_cast<NodeID>(nodeId), node));
 
 			if (significant) {
+				// For tagged nodes, call Lua, then save the OutputObject
+				boost::container::flat_map<std::string, std::string> tags;
+				tags.reserve(kvPos / 2);
+
 				for (uint n=kvStart; n<kvPos-1; n+=2) {
 					tags[pb.stringtable().s(dense.keys_vals(n))] = pb.stringtable().s(dense.keys_vals(n+1));
 				}