diff --git a/src/ncp/spinel.h b/src/ncp/spinel.h
index d1ad55928..2d2663d76 100644
--- a/src/ncp/spinel.h
+++ b/src/ncp/spinel.h
@@ -28,6 +28,7 @@
 #ifndef SPINEL_HEADER_INCLUDED
 #define SPINEL_HEADER_INCLUDED 1
 
+#include <stdarg.h>
 #include <stdio.h>
 #include <stdbool.h>
 #include <stdint.h>