diff --git a/01-tree_successor/cpp/Makefile b/01-tree_successor/cpp/Makefile
index 45d4edb0e4cfdfd86c3339d9ecd0958a31b3b232..44ba78de97fe342742c3d07e3827ab9ca90cd03a 100644
--- a/01-tree_successor/cpp/Makefile
+++ b/01-tree_successor/cpp/Makefile
@@ -1,7 +1,7 @@
 test: tree_successor_test
 	./$<
 
-CXXFLAGS=-O2 -Wall -Wextra -g -Wno-sign-compare
+CXXFLAGS=-std=gnu++11 -O2 -Wall -Wextra -g -Wno-sign-compare
 
 tree_successor_test: tree_successor.h tree_successor_test.cpp test_main.cpp
 	$(CXX) $(CXXFLAGS) $^ -o $@