diff --git a/programs/pkey/pk_sign.c b/programs/pkey/pk_sign.c
index f3bcdb2..554fdf4 100644
--- a/programs/pkey/pk_sign.c
+++ b/programs/pkey/pk_sign.c
@@ -20,6 +20,7 @@
 #include "mbedtls/build_info.h"
 
 #include "mbedtls/platform.h"
+#include "mbedtls/md.h"
 
 #if !defined(MBEDTLS_BIGNUM_C) || !defined(MBEDTLS_ENTROPY_C) ||  \
     !defined(MBEDTLS_MD_CAN_SHA256) || !defined(MBEDTLS_MD_C) || \