diff --git a/include/xgboost/tree_updater.h b/include/xgboost/tree_updater.h
index b5e0a96a8..5f5dd5ecf 100644
--- a/include/xgboost/tree_updater.h
+++ b/include/xgboost/tree_updater.h
@@ -9,6 +9,7 @@
 #define XGBOOST_TREE_UPDATER_H_
 
 #include <dmlc/registry.h>
+#include <functional>
 #include <vector>
 #include <utility>
 #include <string>
@@ -16,10 +17,6 @@
 #include "./data.h"
 #include "./tree_model.h"
 
-#ifdef _MSC_VER
-#include <functional>
-#endif
-
 namespace xgboost {
 /*!
  * \brief interface of tree update module, that performs update of a tree.
diff --git a/src/data/sparse_batch_page.h b/src/data/sparse_batch_page.h
index 9951fbe1d..8c111a840 100644
--- a/src/data/sparse_batch_page.h
+++ b/src/data/sparse_batch_page.h
@@ -17,16 +17,13 @@
 #include <string>
 #include <utility>
 #include <memory>
+#include <functional>
 
 #if DMLC_ENABLE_STD_THREAD
 #include <dmlc/concurrency.h>
 #include <thread>
 #endif
 
-#ifdef _MSC_VER
-#include <functional>
-#endif
-
 namespace xgboost {
 namespace data {
 /*!