diff --git a/include/mbedtls/x509.h b/include/mbedtls/x509.h
index 7faf176..ba2396a 100644
--- a/include/mbedtls/x509.h
+++ b/include/mbedtls/x509.h
@@ -27,6 +27,7 @@
 
 #include "mbedtls/asn1.h"
 #include "mbedtls/pk.h"
+#include "pk_internal.h"
 
 #if defined(MBEDTLS_RSA_C)
 #include "mbedtls/rsa.h"