diff --git a/cpp/QrCode.cpp b/cpp/QrCode.cpp
index aca04b0..4ed4153 100644
--- a/cpp/QrCode.cpp
+++ b/cpp/QrCode.cpp
@@ -24,6 +24,7 @@
 #include <algorithm>
 #include <climits>
 #include <cstddef>
+#include <cstdlib>
 #include <sstream>
 #include "BitBuffer.hpp"
 #include "QrCode.hpp"