diff --git a/test/unit/core/test_def.c b/test/unit/core/test_def.c
index e8ec63a6..31088494 100644
--- a/test/unit/core/test_def.c
+++ b/test/unit/core/test_def.c
@@ -2,7 +2,7 @@
 
 #include "lwip/def.h"
 
-#define MAGIC_UNTOUCHED_BYTE  0xfa
+#define MAGIC_UNTOUCHED_BYTE  0x7a
 #define TEST_BUFSIZE          32
 #define GUARD_SIZE            4