diff --git a/src/bench.cpp b/src/bench.cpp
index d9a3b54f2f3aaf09700fbc67a36f28a986e0b08d..04c372d8fc38f404d146c0451481a4cee7c506ae 100644
--- a/src/bench.cpp
+++ b/src/bench.cpp
@@ -101,7 +101,7 @@ TEST_CASE("Canonical cubic EOS derivatives", "[cubic]")
     auto model = canonical_PR(Tc_K, pc_Pa, acentric);
 
     double T = 300, rho = 2;
-    std::valarray<double> z(2, 1.0);
+    std::valarray<double> z = { 0.5, 0.3, 0.2 };
     using tdx = TDXDerivatives<decltype(model), double, decltype(z)>;
 
     BENCHMARK("alphar") {