diff --git a/library/x509.c b/library/x509.c
index 9d00beb..0a9138f 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -38,6 +38,7 @@
 #if defined(MBEDTLS_X509_USE_C)
 
 #include "mbedtls/x509.h"
+#include "mbedtls/x509_internal.h"
 #include "mbedtls/asn1.h"
 #include "mbedtls/oid.h"