diff --git a/library/x509_csr.c b/library/x509_csr.c
index ad49abc..826eafd 100644
--- a/library/x509_csr.c
+++ b/library/x509_csr.c
@@ -51,6 +51,7 @@
 #include "polarssl/platform.h"
 #else
 #include <stdlib.h>
+#include <stdio.h>
 #define polarssl_free       free
 #define polarssl_malloc     malloc
 #define polarssl_snprintf   snprintf