diff --git a/lib/base64.c b/lib/base64.c
index 02778fa0c6..4ffd7605bc 100644
--- a/lib/base64.c
+++ b/lib/base64.c
@@ -37,6 +37,10 @@
 #endif
 #include <stdlib.h>
 #include <string.h>
+
+#define _MPRINTF_REPLACE /* use our functions only */
+#include <curl/mprintf.h>
+
 #include "base64.h"
 
 #ifdef MALLOCDEBUG