diff --git a/sa.hpp b/sa.hpp
index 44a7f19..4e7c45f 100644
--- a/sa.hpp
+++ b/sa.hpp
@@ -94,7 +94,7 @@ class box {
 
 class solution {
 	std::vector<box> boxes;
-	std::default_random_engine gen;
+	std::mt19937_64 gen;
 	long long fitness;
 	int capacity;
 	int iterations;