diff --git a/src/util.c b/src/util.c
index 46e7bd3..17430c4 100644
--- a/src/util.c
+++ b/src/util.c
@@ -71,7 +71,7 @@ reverse_hex(char *hex, size_t len)
 {
     assert(len % 2 == 0);
     size_t start = 0;
-    size_t end = len-1;
+    size_t end = len-2;
     char temp[2];
     while (start < end)
     {