diff --git a/R-package/src/Makevars b/R-package/src/Makevars
index 289f1a15a..5cea1438c 100644
--- a/R-package/src/Makevars
+++ b/R-package/src/Makevars
@@ -4,4 +4,4 @@ PKGROOT=../../
 PKG_CPPFLAGS= -DXGBOOST_CUSTOMIZE_MSG_ -DXGBOOST_CUSTOMIZE_PRNG_ -DXGBOOST_STRICT_CXX98_ -I$(PKGROOT)
 PKG_CXXFLAGS= $(SHLIB_OPENMP_CFLAGS)
 PKG_LIBS = $(SHLIB_OPENMP_CFLAGS)
-OBJECTS= xgboost_R.o xgboost_assert.o $(PKGROOT)/wrapper/xgboost_wrapper.o $(PKGROOT)/src/io/io.o $(PKGROOT)/src/gbm/gbm.o $(PKGROOT)/src/tree/updater.o
+OBJECTS= xgboost_R.o xgboost_assert.o $(PKGROOT)/wrapper/xgboost_wrapper.o $(PKGROOT)/src/io/io.o $(PKGROOT)/src/gbm/gbm.o $(PKGROOT)/src/tree/updater.o $(PKGROOT)/src/sync/sync_empty.o
diff --git a/R-package/src/Makevars.win b/R-package/src/Makevars.win
index 289f1a15a..5cea1438c 100644
--- a/R-package/src/Makevars.win
+++ b/R-package/src/Makevars.win
@@ -4,4 +4,4 @@ PKGROOT=../../
 PKG_CPPFLAGS= -DXGBOOST_CUSTOMIZE_MSG_ -DXGBOOST_CUSTOMIZE_PRNG_ -DXGBOOST_STRICT_CXX98_ -I$(PKGROOT)
 PKG_CXXFLAGS= $(SHLIB_OPENMP_CFLAGS)
 PKG_LIBS = $(SHLIB_OPENMP_CFLAGS)
-OBJECTS= xgboost_R.o xgboost_assert.o $(PKGROOT)/wrapper/xgboost_wrapper.o $(PKGROOT)/src/io/io.o $(PKGROOT)/src/gbm/gbm.o $(PKGROOT)/src/tree/updater.o
+OBJECTS= xgboost_R.o xgboost_assert.o $(PKGROOT)/wrapper/xgboost_wrapper.o $(PKGROOT)/src/io/io.o $(PKGROOT)/src/gbm/gbm.o $(PKGROOT)/src/tree/updater.o $(PKGROOT)/src/sync/sync_empty.o