diff --git a/src/axis_imu.cc b/src/axis_imu.cc
index 83f3dd6568e47f4832b6f352dcf7017725db25bb..11b5285d18eea5f34935356a76f7fd3c1545251b 100644
--- a/src/axis_imu.cc
+++ b/src/axis_imu.cc
@@ -184,7 +184,7 @@ private:
 
   boost::asio::ip::udp::udp::socket socket_;
   boost::asio::ip::udp::udp::endpoint remote_endpoint_;
-  boost::array<char, 128> recv_buffer_;
+  boost::array<unsigned char, 128> recv_buffer_;
 
   bool have_gyro_flag;
   bool have_acc_flag;