diff --git a/library/x509_oid.c b/library/x509_oid.c
index 3517ee3..e8bd0d1 100644
--- a/library/x509_oid.c
+++ b/library/x509_oid.c
@@ -11,6 +11,7 @@
 
 #if defined(MBEDTLS_OID_C)
 
+#include "mbedtls/oid.h"
 #include "x509_oid.h"
 
 #include <stdio.h>