diff --git a/eth/syncer/syncer.go b/eth/syncer/syncer.go
index 36c4c8a0c7..416bd62ed1 100644
--- a/eth/syncer/syncer.go
+++ b/eth/syncer/syncer.go
@@ -19,13 +19,13 @@ package syncer
 import (
 	"errors"
 	"fmt"
-	"github.com/ethereum/go-ethereum/eth/ethconfig"
 	"sync"
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/eth"
+	"github.com/ethereum/go-ethereum/eth/ethconfig"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/node"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -130,7 +130,7 @@ func (s *Syncer) run() {
 			}
 			if resync {
 				if mode := s.backend.Downloader().GetSyncMode(); mode != ethconfig.FullSync {
-					req.errc <- fmt.Errorf("unsupported syncmode %v", mode)
+					req.errc <- fmt.Errorf("unsupported syncmode %v, please relaunch geth with --syncmode full", mode)
 				} else {
 					req.errc <- s.backend.Downloader().BeaconDevSync(target)
 				}