diff --git a/src/fractal.cpp b/src/fractal.cpp
index 20c0731..cee25b6 100644
--- a/src/fractal.cpp
+++ b/src/fractal.cpp
@@ -19,6 +19,26 @@ token_id_t ruleset_t::add_token(token_type_e type, mtl::fixed value) {
 	return m_tokens.size() - 1;
 }
 
+group_id_t ruleset_t::add_group_characteristic(const etl::ivector<token_id_t>& tokens, uint32_t factor) {
+	if (m_group_characteristics.full()) {
+		throw mtl::length_error();
+	}
+
+	m_group_characteristics.push_back(group_characteristic_t());
+	group_characteristic_t& chr = m_group_characteristics.back();
+	chr.m_factor = factor;
+
+	for (token_id_t tok : tokens) {
+		if (!valid_token(tok)) {
+			throw mtl::invalid_argument();
+		}
+
+		chr.m_token_ids.push_back(tok);
+	}
+
+	return m_group_characteristics.size() - 1;
+}
+
 #if 0
 token_id_t generator_t::add_token(token_type_e type, mtl::fixed value) {
 	log::debug << "Adding token with type " << (int)type << endl;