diff --git a/StructuralGasEstimator.cpp b/StructuralGasEstimator.cpp
index 2cf8c2a81..c90981a72 100644
--- a/StructuralGasEstimator.cpp
+++ b/StructuralGasEstimator.cpp
@@ -31,7 +31,7 @@ using namespace dev;
 using namespace dev::eth;
 using namespace dev::solidity;
 
-map<ASTNode const*, GasMeter::GasConsumption[2]> StructuralGasEstimator::performEstimation(
+StructuralGasEstimator::ASTGasConsumptionSelfAccumulated StructuralGasEstimator::performEstimation(
 	AssemblyItems const& _items,
 	vector<ASTNode const*> const& _ast
 )
@@ -42,7 +42,7 @@ map<ASTNode const*, GasMeter::GasConsumption[2]> StructuralGasEstimator::perform
 	for (auto const& item: _items)
 		particularCosts[item.getLocation()] += meter.estimateMax(item);
 
-	map<ASTNode const*, GasMeter::GasConsumption[2]> gasCosts;
+	ASTGasConsumptionSelfAccumulated gasCosts;
 	auto onNode = [&](ASTNode const& _node)
 	{
 		gasCosts[&_node][0] = gasCosts[&_node][1] = particularCosts[_node.getLocation()];
@@ -60,7 +60,7 @@ map<ASTNode const*, GasMeter::GasConsumption[2]> StructuralGasEstimator::perform
 }
 
 map<ASTNode const*, GasMeter::GasConsumption> StructuralGasEstimator::breakToStatementLevel(
-	map<ASTNode const*, GasMeter::GasConsumption[2]> const& _gasCosts,
+	ASTGasConsumptionSelfAccumulated const& _gasCosts,
 	vector<ASTNode const*> const& _roots
 )
 {
diff --git a/StructuralGasEstimator.h b/StructuralGasEstimator.h
index b9e976432..df1ae509d 100644
--- a/StructuralGasEstimator.h
+++ b/StructuralGasEstimator.h
@@ -24,6 +24,7 @@
 
 #include <vector>
 #include <map>
+#include <array>
 #include <libsolidity/ASTForward.h>
 #include <libevmasm/GasMeter.h>
 #include <libevmasm/Assembly.h>
@@ -37,11 +38,13 @@ class StructuralGasEstimator
 {
 public:
 	using ASTGasConsumption = std::map<ASTNode const*, eth::GasMeter::GasConsumption>;
+	using ASTGasConsumptionSelfAccumulated =
+		std::map<ASTNode const*, std::array<eth::GasMeter::GasConsumption, 2>>;
 
 	/// Estimates the gas consumption for every assembly item in the given assembly and stores
 	/// it by source location.
 	/// @returns a mapping from each AST node to a pair of its particular and syntactically accumulated gas costs.
-	std::map<ASTNode const*, eth::GasMeter::GasConsumption[2]> performEstimation(
+	ASTGasConsumptionSelfAccumulated performEstimation(
 		eth::AssemblyItems const& _items,
 		std::vector<ASTNode const*> const& _ast
 	);
@@ -50,7 +53,7 @@ public:
 	/// 1. source locations of statements that do not contain other statements
 	/// 2. maximal source locations that do not overlap locations coming from the first rule
 	ASTGasConsumption breakToStatementLevel(
-		std::map<ASTNode const*, eth::GasMeter::GasConsumption[2]> const& _gasCosts,
+		ASTGasConsumptionSelfAccumulated const& _gasCosts,
 		std::vector<ASTNode const*> const& _roots
 	);
 };