diff --git a/eis_regular_data.c b/eis_regular_data.c
index f52bbdb..7c94a76 100644
--- a/eis_regular_data.c
+++ b/eis_regular_data.c
@@ -196,7 +196,7 @@ static void regular_data_msg_task(void *pArg)
                     chksum += payload.raw[i];
                 }
                 /* append checksum */
-                payload.raw[payload.header.len + 1] = chksum;
+                payload.raw[payload.header.len] = chksum;
                 /* try to send notify */
                 ret_code_t err_code = le_regular_data_notify(payload.raw, payload.header.len + 1);
                 /* if notify success, breaks out of the loop. */