diff --git a/src/ncp/hdlc.hpp b/src/ncp/hdlc.hpp
index 9e88af2b7..aacbd5737 100644
--- a/src/ncp/hdlc.hpp
+++ b/src/ncp/hdlc.hpp
@@ -37,6 +37,7 @@
 
 #include <stdint.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include <openthread/error.h>
 #include "common/code_utils.hpp"