diff --git a/src/thermophysicalModels/specie/equationOfState/perfectGas/perfectGasI.H b/src/thermophysicalModels/specie/equationOfState/perfectGas/perfectGasI.H
index 94e0c500ffcdfe4ee47d8c9b02a1ba05a06f9e69..67a75fdb4013aaa9a2cf75b6661e2773f65c5c9e 100644
--- a/src/thermophysicalModels/specie/equationOfState/perfectGas/perfectGasI.H
+++ b/src/thermophysicalModels/specie/equationOfState/perfectGas/perfectGasI.H
@@ -24,6 +24,9 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "perfectGas.H"
+#include "thermodynamicConstants.H"
+
+using namespace Foam::constant::thermodynamic;
 
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //