diff --git a/src/or/eventdns.c b/src/or/eventdns.c
index 4464148141..4ae17a40c3 100644
--- a/src/or/eventdns.c
+++ b/src/or/eventdns.c
@@ -1842,7 +1842,7 @@ evdns_server_request_format_response(struct server_request *req, int err)
 	if (j > 512) {
 overflow:
 		j = 512;
-		buf[3] |= 0x02; /* set the truncated bit. */
+		buf[2] |= 0x02; /* set the truncated bit. */
 	}
 
 	req->response_len = (size_t)j;