diff --git a/library/x509write.c b/library/x509write.c
index d434df5..4704900 100644
--- a/library/x509write.c
+++ b/library/x509write.c
@@ -8,6 +8,7 @@
 #if defined(MBEDTLS_X509_CSR_WRITE_C) || defined(MBEDTLS_X509_CRT_WRITE_C)
 
 #include "mbedtls/x509_crt.h"
+#include "x509_internal.h"
 #include "mbedtls/asn1write.h"
 #include "mbedtls/error.h"
 #include "mbedtls/oid.h"