diff --git a/src/sat_Z_accuracy.cpp b/src/sat_Z_accuracy.cpp
index 8d0517009eb278fbe09f5ee8b67e90778096fb51..fa68045e52a03438b9974e0a58bfeafeba9202b3 100644
--- a/src/sat_Z_accuracy.cpp
+++ b/src/sat_Z_accuracy.cpp
@@ -150,7 +150,7 @@ auto with_teqp_and_boost(const Model &model, double T, double rho, const VECTOR
     calc_output o;
     o.Zexact = static_cast<double>(Zexact);
     o.Zteqp = Zteqp;
-    o.Ar01exact = derL3;
+    o.Ar01exact = static_cast<double>(derL3);
     o.Ar01teqp = Ar01teqp;
 
     // Now do the third-order derivative of alphar, as a further test