diff --git a/src/TestProblem/Hydro/ClusterMerger/Init_TestProb_ClusterMerger.cpp b/src/TestProblem/Hydro/ClusterMerger/Init_TestProb_ClusterMerger.cpp
index ee7c8e40a3..cd8dc5b7af 100644
--- a/src/TestProblem/Hydro/ClusterMerger/Init_TestProb_ClusterMerger.cpp
+++ b/src/TestProblem/Hydro/ClusterMerger/Init_TestProb_ClusterMerger.cpp
@@ -62,6 +62,10 @@ static FieldIdx_t ColorField3Idx = Idx_Undefined;
 
 // problem-specific function prototypes
 #ifdef MASSIVE_PARTICLES
+int ParHaloIdx = Idx_Undefined;
+
+void AddNewParticleAttribute_ClusterMerger();
+
 long Read_Particle_Number_ClusterMerger(std::string filename);
 void Par_Init_ByFunction_ClusterMerger(const long NPar_ThisRank,
                                        const long NPar_AllRank,
@@ -113,6 +117,9 @@ void Validate()
    Aux_Error( ERROR_INFO, "COMOVING must be disabled !!\n" );
 #  endif
 
+   if ( PAR_NATT_USER != 1 ) 
+      Aux_Error( ERROR_INFO, "PAR_NATT_USER must be set to 1 in the Makefile!!");
+
    if ( !OPT__UNIT )
       Aux_Error( ERROR_INFO, "OPT__UNIT must be enabled !!\n" );
 
@@ -124,7 +131,7 @@ void Validate()
    if ( OPT__BC_POT == BC_POT_PERIODIC )
       Aux_Error( ERROR_INFO, "do not use periodic BC (OPT__BC_POT = 1) for this test !!\n" );
 #  endif
-
+   
 #  ifdef MASSIVE_PARTICLES
    if ( OPT__INIT == INIT_BY_FUNCTION  &&  amr->Par->Init != PAR_INIT_BY_FUNCTION )
       Aux_Error( ERROR_INFO, "please set PAR_INIT = 1 (by FUNCTION) !!\n" );
@@ -692,7 +699,7 @@ void Init_TestProb_Hydro_ClusterMerger()
    End_User_Ptr                   = End_ClusterMerger;
    Par_Init_ByFunction_Ptr        = Par_Init_ByFunction_ClusterMerger;
    Init_Field_User_Ptr            = AddNewField_ClusterMerger;
-   //Par_Init_Attribute_User_Ptr    = AddNewParticleAttribute_ClusterMerger;
+   Par_Init_Attribute_User_Ptr    = AddNewParticleAttribute_ClusterMerger;
 #  ifdef MHD
    Init_Function_BField_User_Ptr  = SetBFieldIC;
 #  endif
@@ -785,4 +792,15 @@ void AddNewField_ClusterMerger()
 
 }
 
+#endif
+
+#ifdef MASSIVE_PARTICLES
+
+void AddNewParticleAttribute_ClusterMerger()
+{
+  if ( ParHaloIdx == Idx_Undefined )
+    ParHaloIdx = AddParticleAttribute( "ParHalo" );
+}
+
+
 #endif
diff --git a/src/TestProblem/Hydro/ClusterMerger/Par_Init_ByFunction_ClusterMerger.cpp b/src/TestProblem/Hydro/ClusterMerger/Par_Init_ByFunction_ClusterMerger.cpp
index 84c7533181..f5d973168f 100644
--- a/src/TestProblem/Hydro/ClusterMerger/Par_Init_ByFunction_ClusterMerger.cpp
+++ b/src/TestProblem/Hydro/ClusterMerger/Par_Init_ByFunction_ClusterMerger.cpp
@@ -31,6 +31,9 @@ extern long    NPar_AllCluster;
 
 
 #ifdef MASSIVE_PARTICLES
+
+extern int ParHaloIdx;
+
 void Read_Particles_ClusterMerger(std::string filename, long offset, long num,
                                   real_par_in xpos[], real_par_in ypos[],
                                   real_par_in zpos[], real_par_in xvel[],
@@ -217,6 +220,9 @@ void Par_Init_ByFunction_ClusterMerger( const long NPar_ThisRank, const long NPa
          // synchronize all particles to the physical time at the base level
          ParTime[pp] = (real_par)Time[0];
 
+	 // Set tag for each cluster
+	 AllAttribute[ParHaloIdx][pp] = real( c );
+
       }
 
       delete [] mass;