diff --git a/library/x509_csr.c b/library/x509_csr.c
index 23af9ae..9b58a86 100644
--- a/library/x509_csr.c
+++ b/library/x509_csr.c
@@ -38,6 +38,7 @@
 #if defined(MBEDTLS_X509_CSR_PARSE_C)
 
 #include "mbedtls/x509_csr.h"
+#include "mbedtls/x509_internal.h"
 #include "mbedtls/oid.h"
 #include "mbedtls/platform_util.h"