diff --git a/dumux/porousmediumflow/2p1c/indices.hh b/dumux/porousmediumflow/2p1c/indices.hh
index 15d5959f23e3422a484941ebb5b273e7b5e8840b..d53be4494b6666e4d3fa0c6bffd440bbf3f3f319 100644
--- a/dumux/porousmediumflow/2p1c/indices.hh
+++ b/dumux/porousmediumflow/2p1c/indices.hh
@@ -46,6 +46,8 @@ public:
     // Equation indices
     static const int conti0EqIdx = 0; //!< Index of the mass conservation equation for the water component.
     static const int energyEqIdx = 1; //<! The index for energy in equation vectors.
+
+    static const int temperatureIdx = -99; //!< For compatibility reasons. Do not use.
 };
 
 } // end namespace Dumux