diff --git a/library/x509write_csr.c b/library/x509write_csr.c
index d70ba0e..85331b1 100644
--- a/library/x509write_csr.c
+++ b/library/x509write_csr.c
@@ -33,6 +33,7 @@
 #if defined(MBEDTLS_X509_CSR_WRITE_C)
 
 #include "mbedtls/x509_csr.h"
+#include "mbedtls/x509_internal.h"
 #include "mbedtls/oid.h"
 #include "mbedtls/asn1write.h"
 #include "mbedtls/platform_util.h"