diff --git a/src/tree/param.h b/src/tree/param.h
index aab11ad1e..4a7c790a6 100644
--- a/src/tree/param.h
+++ b/src/tree/param.h
@@ -57,7 +57,7 @@ struct TrainParam{
     opt_dense_col = 1.0f;
     nthread = 0;
     size_leaf_vector = 0;
-    parallel_option = 0;
+    parallel_option = 2;
   }
   /*! 
    * \brief set parameters from outside 
diff --git a/src/tree/updater_colmaker-inl.hpp b/src/tree/updater_colmaker-inl.hpp
index 1ccf32a41..9c2740264 100644
--- a/src/tree/updater_colmaker-inl.hpp
+++ b/src/tree/updater_colmaker-inl.hpp
@@ -418,7 +418,11 @@ class ColMaker: public IUpdater {
       #if defined(_OPENMP)                                                                
       const int batch_size = std::max(static_cast<int>(nsize / this->nthread / 32), 1);
       #endif
-      if (param.parallel_option == 0) {
+      int poption = param.parallel_option;
+      if (poption == 2) {
+        poption = nsize * 2 < nthread ? 1 : 0;
+      }
+      if (poption == 0) {
         #pragma omp parallel for schedule(dynamic, batch_size)
         for (bst_omp_uint i = 0; i < nsize; ++i) {
           const bst_uint fid = batch.col_index[i];