diff --git a/src/data.h b/src/data.h
index f85b69034..1c9d9a290 100644
--- a/src/data.h
+++ b/src/data.h
@@ -373,8 +373,8 @@ class FMatrixS : public FMatrixInterface<FMatrixS>{
     unsigned ncol = static_cast<unsigned>(this->NumCol());
     #pragma omp parallel for schedule(static)
     for (unsigned i = 0; i < ncol; ++i) {
-      std::sort(&col_data_[col_ptr_[i]],
-                &col_data_[col_ptr_[i + 1]], Entry::CmpValue);
+      std::sort(&col_data_[0] + col_ptr_[i],
+                &col_data_[0] + col_ptr_[i + 1], Entry::CmpValue);
     }
   }
 
diff --git a/src/tree/model.h b/src/tree/model.h
index f91e453f8..d565effe6 100644
--- a/src/tree/model.h
+++ b/src/tree/model.h
@@ -259,10 +259,12 @@ class TreeModel {
   }
   /*! \brief get leaf vector given nid */
   inline bst_float* leafvec(int nid) {
+    if (leaf_vector.size() == 0) return NULL;
     return &leaf_vector[nid * param.size_leaf_vector];
   }
   /*! \brief get leaf vector given nid */
   inline const bst_float* leafvec(int nid) const{
+    if (leaf_vector.size() == 0) return NULL;
     return &leaf_vector[nid * param.size_leaf_vector];
   }
   /*! \brief initialize the model */