diff --git a/library/x509_csr.c b/library/x509_csr.c
index 0a77bef..32a3bb2 100644
--- a/library/x509_csr.c
+++ b/library/x509_csr.c
@@ -21,6 +21,7 @@
 
 #include "mbedtls/x509_csr.h"
 #include "mbedtls/error.h"
+#include "mbedtls/oid.h"
 #include "x509_oid.h"
 #include "mbedtls/platform_util.h"