diff --git a/src/thermophysicalModels/specie/equationOfState/perfectFluid/perfectFluidI.H b/src/thermophysicalModels/specie/equationOfState/perfectFluid/perfectFluidI.H
index 770ed5a2ef..9204872f40 100644
--- a/src/thermophysicalModels/specie/equationOfState/perfectFluid/perfectFluidI.H
+++ b/src/thermophysicalModels/specie/equationOfState/perfectFluid/perfectFluidI.H
@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     | Website:  https://openfoam.org
-    \\  /    A nd           | Copyright (C) 2012-2018 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2012-2019 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -101,7 +101,9 @@ inline Foam::scalar Foam::perfectFluid<Specie>::H(scalar p, scalar T) const
 template<class Specie>
 inline Foam::scalar Foam::perfectFluid<Specie>::Cp(scalar p, scalar T) const
 {
-    return 0;
+    return
+        sqr(p/(rho(p, T)*T))/this->R()
+      - sqr(Pstd/(rho(Pstd, T)*T))/this->R();
 }