diff --git a/library/x509_crt.c b/library/x509_crt.c
index 0b0e8d1..0a43d87 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -23,6 +23,7 @@
 
 #include "mbedtls/x509_crt.h"
 #include "mbedtls/error.h"
+#include "mbedtls/oid.h"
 #include "x509_oid.h"
 #include "mbedtls/platform_util.h"