diff --git a/tests/Makefile b/tests/Makefile
index c935b00..cba1143 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -1,5 +1,5 @@
 
-CXXFLAGS = -I.. -std=c++17 -W -Wall -Ofast -fno-exceptions -fno-rtti -march=native
+CXXFLAGS = -I.. -std=c++11 -W -Wall -Ofast -fno-exceptions -fno-rtti -march=native
 CXX = clang++ -stdlib=libc++
 #CXX = g++
 
diff --git a/tests/bch_decoder_test.cc b/tests/bch_decoder_test.cc
index ac437db..8bcbdfb 100644
--- a/tests/bch_decoder_test.cc
+++ b/tests/bch_decoder_test.cc
@@ -7,6 +7,7 @@ Copyright 2018 Ahmet Inan <inan@aicodix.de>
 #include <cassert>
 #include <random>
 #include <iostream>
+#include <functional>
 #include "bitman.hh"
 #include "galois_field.hh"
 #include "bose_chaudhuri_hocquenghem_decoder.hh"
diff --git a/tests/bch_regression_test.cc b/tests/bch_regression_test.cc
index 93efb61..393b5cd 100644
--- a/tests/bch_regression_test.cc
+++ b/tests/bch_regression_test.cc
@@ -7,6 +7,7 @@ Copyright 2018 Ahmet Inan <inan@aicodix.de>
 #include <cassert>
 #include <random>
 #include <iostream>
+#include <functional>
 #include "galois_field.hh"
 #include "bose_chaudhuri_hocquenghem_encoder.hh"
 #include "bose_chaudhuri_hocquenghem_decoder.hh"
diff --git a/tests/rs_decoder_test.cc b/tests/rs_decoder_test.cc
index bb7e417..e4eec07 100644
--- a/tests/rs_decoder_test.cc
+++ b/tests/rs_decoder_test.cc
@@ -7,6 +7,7 @@ Copyright 2018 Ahmet Inan <inan@aicodix.de>
 #include <cassert>
 #include <random>
 #include <iostream>
+#include <functional>
 #include "galois_field.hh"
 #include "reed_solomon_decoder.hh"
 
diff --git a/tests/rs_regression_test.cc b/tests/rs_regression_test.cc
index 944ef92..be91edb 100644
--- a/tests/rs_regression_test.cc
+++ b/tests/rs_regression_test.cc
@@ -7,6 +7,7 @@ Copyright 2018 Ahmet Inan <inan@aicodix.de>
 #include <cassert>
 #include <random>
 #include <iostream>
+#include <functional>
 #include "galois_field.hh"
 #include "reed_solomon_encoder.hh"
 #include "reed_solomon_decoder.hh"