diff --git a/library/x509write_csr.c b/library/x509write_csr.c
index f3dc9d9..b353d37 100644
--- a/library/x509write_csr.c
+++ b/library/x509write_csr.c
@@ -17,6 +17,7 @@
 #include "mbedtls/x509_csr.h"
 #include "mbedtls/asn1write.h"
 #include "mbedtls/error.h"
+#include "mbedtls/oid.h"
 #include "x509_oid.h"
 #include "mbedtls/platform_util.h"