diff --git a/src/tree/tree_model.cc b/src/tree/tree_model.cc
index f42624bbe..ec4beaddd 100644
--- a/src/tree/tree_model.cc
+++ b/src/tree/tree_model.cc
@@ -868,7 +868,8 @@ void RegTree::Save(dmlc::Stream* fo) const {
   CHECK_EQ(param.num_nodes, static_cast<int>(stats_.size()));
   CHECK_EQ(param.deprecated_num_roots, 1);
   CHECK_NE(param.num_nodes, 0);
-  CHECK(!HasCategoricalSplit()) << "Please JSON/UBJSON for saving models with categorical splits.";
+  CHECK(!HasCategoricalSplit())
+      << "Please use JSON/UBJSON for saving models with categorical splits.";
 
   if (DMLC_IO_NO_ENDIAN_SWAP) {
     fo->Write(&param, sizeof(TreeParam));