diff --git a/dumux/material/fluidsystems/1padapter.hh b/dumux/material/fluidsystems/1padapter.hh
index d849958da6f88ed02fd211a75ae499b84afcf832..82d45f8b632bf182e1572c70259e5ea0ddad74b0 100644
--- a/dumux/material/fluidsystems/1padapter.hh
+++ b/dumux/material/fluidsystems/1padapter.hh
@@ -85,6 +85,8 @@ public:
 
     //! export the wrapped MultiPhaseFluidSystem type
     using MultiPhaseFluidSystem = MPFluidSystem;
+    //! the index of the phase we choose from the multi-phase fluid system
+    static constexpr int multiphaseFluidsystemPhaseIdx = phase;
 
     //! number of phases in the fluid system
     static constexpr int numPhases = 1;