diff --git a/lib/hx509/hx509.h b/lib/hx509/hx509.h
index 3099f4cc7..6d0b40334 100644
--- a/lib/hx509/hx509.h
+++ b/lib/hx509/hx509.h
@@ -38,6 +38,7 @@
 
 #include <rfc2459_asn1.h>
 #include <stdarg.h>
+#include <stdio.h>
 
 typedef struct hx509_cert_attribute_data *hx509_cert_attribute;
 typedef struct hx509_cert_data *hx509_cert;