diff --git a/tests/libtest/lib1515.c b/tests/libtest/lib1515.c
index d5c8f7d08..a786addb7 100644
--- a/tests/libtest/lib1515.c
+++ b/tests/libtest/lib1515.c
@@ -39,6 +39,9 @@
 #define sleep(s) Sleep(s * 1000)
 #endif
 
+#define _MPRINTF_REPLACE
+#include "mprintf.h"
+
 static int debug_callback(CURL *curl, curl_infotype info, char *msg, size_t len, void *ptr)
 {
   (void)curl;