diff --git a/dtmcli/barrier.go b/dtmcli/barrier.go
index 251611d..898f831 100644
--- a/dtmcli/barrier.go
+++ b/dtmcli/barrier.go
@@ -8,6 +8,7 @@ package dtmcli
 
 import (
 	"database/sql"
+	"errors"
 	"fmt"
 	"net/url"
 
@@ -82,6 +83,10 @@ func (bb *BranchBarrier) Call(tx *sql.Tx, busiCall BarrierBusiFunc) (rerr error)
 		rerr = oerr
 	}
 
+	if bb.Op == "msg" && currentAffected == 0 { // for msg's DoAndSubmit, repeated insert should be rejected.
+		return errors.New("unique key conflict")
+	}
+
 	if (ti.Op == BranchCancel || ti.Op == BranchCompensate) && originAffected > 0 || // null compensate
 		currentAffected == 0 { // repeated request or dangled request
 		return