diff --git a/src/cltools/SumHills.cpp b/src/cltools/SumHills.cpp
index 5f865546f3a692b93194b8057f2f53f002fe26b8..8063239fcf007f966e19e761e8fe3f108e4ea461 100644
--- a/src/cltools/SumHills.cpp
+++ b/src/cltools/SumHills.cpp
@@ -453,6 +453,10 @@ int CLToolSumHills::main(FILE* in,FILE*out,Communicator& pc){
   if(grid_has_bin){
      addme="GRID_BIN="; for(unsigned i=0;i<(ncv-1);i++)addme+=gbin[i]+","; addme+=gbin[ncv-1];
      actioninput.push_back(addme);
+  }else{
+	  //automatic bin: 50 per dimension;
+	  addme="GRID_BIN="; for(unsigned i=0;i<(ncv-1);i++)addme+="50,"; addme+="50";
+	  actioninput.push_back(addme);
   }
   std::string  stride; stride="";
   if(parse("--stride",stride)){