diff --git a/programs/pkey/pk_verify.c b/programs/pkey/pk_verify.c
index a6bfe3f..f80bf64 100644
--- a/programs/pkey/pk_verify.c
+++ b/programs/pkey/pk_verify.c
@@ -52,6 +52,7 @@
 #include "mbedtls/error.h"
 #include "mbedtls/md.h"
 #include "mbedtls/pk.h"
+#include "mbedtls/bignum.h"
 
 #include <stdio.h>
 #include <string.h>