diff --git a/src/ifcparse/IfcEntityInstanceData.cpp b/src/ifcparse/IfcEntityInstanceData.cpp
index 222d7ee1f3..201701b6ed 100644
--- a/src/ifcparse/IfcEntityInstanceData.cpp
+++ b/src/ifcparse/IfcEntityInstanceData.cpp
@@ -285,7 +285,6 @@ bool impl::serialize(std::string& val, const aggregate_of_aggregate_of_instance:
     std::ostringstream oss;
 	oss.put(TypeEncoder::encode_type<aggregate_of_aggregate_of_instance::ptr>());
     
-	// size of outer aggregate
     auto write_size = [&oss](size_t sz) {
         std::string size_str;
         size_str.resize(sizeof(size_t));
@@ -293,11 +292,11 @@ bool impl::serialize(std::string& val, const aggregate_of_aggregate_of_instance:
         oss.write(size_str.data(), size_str.size());
     };
 
-	write_size(t->size());
+	// write_size(t->size());
 
     for (auto it = t->begin(); it != t->end(); ++it) {
 		// size of inner aggregate
-        write_size(it->size());
+        write_size(it->size() * 9);
 
         // values
         for (auto jt = it->begin(); jt != it->end(); ++jt) {
@@ -409,9 +408,9 @@ bool impl::deserialize(IfcParse::impl::rocks_db_file_storage* storage, const std
 	t.reset(new aggregate_of_aggregate_of_instance);
 	char const* ptr = val.data() + 1;
 
-	size_t outer_size;
-	memcpy(&outer_size, ptr, sizeof(size_t));
-	ptr += sizeof(size_t);
+	// size_t outer_size;
+	// memcpy(&outer_size, ptr, sizeof(size_t));
+	// ptr += sizeof(size_t);
 
     while (ptr < val.data() + val.size()) {
 		size_t inner_size;
diff --git a/src/serializers/RocksDbSerializer.cpp b/src/serializers/RocksDbSerializer.cpp
index 789e72af15..b30cd59530 100644
--- a/src/serializers/RocksDbSerializer.cpp
+++ b/src/serializers/RocksDbSerializer.cpp
@@ -72,8 +72,42 @@ namespace {
 
 	bool serialize(std::string& val, const std::vector<std::vector<IfcParse::reference_or_simple_type>>& t)
 	{
-		// @todo
-		return false;
+		std::ostringstream oss;
+		oss.put(TypeEncoder::encode_type<aggregate_of_aggregate_of_instance::ptr>());
+
+		auto write_size = [&oss](size_t sz) {
+			std::string size_str;
+			size_str.resize(sizeof(size_t));
+			memcpy(size_str.data(), &sz, sizeof(size_t));
+			oss.write(size_str.data(), size_str.size());
+		};
+
+		// write_size(t.size());
+
+		for (auto it = t.begin(); it != t.end(); ++it) {
+			// size of inner aggregate
+			write_size(it->size() * 9);
+
+			// values
+			for (auto jt = it->begin(); jt != it->end(); ++jt) {
+				char c = jt->index() == 0 ? 'i' : 't';
+				oss.put(c);
+				size_t iden = 0;
+				if (auto* name = std::get_if<IfcParse::InstanceReference>(&*jt)) {
+					iden = *name;
+				} else if (auto* inst = std::get_if<IfcUtil::IfcBaseClass*>(&*jt)) {
+					iden = (*inst)->identity();
+				}
+				std::string iden_str;
+				iden_str.resize(sizeof(size_t));
+				memcpy(iden_str.data(), &iden, sizeof(size_t));
+				oss.write(iden_str.data(), iden_str.size());
+			}
+		}
+
+		val = oss.str();
+
+		return true;
 	}
 }