diff --git a/weed/mount/weedfs_write.go b/weed/mount/weedfs_write.go
index 0bcc6f21d..dfe5a6e48 100644
--- a/weed/mount/weedfs_write.go
+++ b/weed/mount/weedfs_write.go
@@ -26,12 +26,14 @@ func (wfs *WFS) saveDataAsChunk(fullPath util.FullPath) filer.SaveDataAsChunkFun
 			return
 		}
 
+		// WantMd5 gives mount writes a real filer.ETag (server echoes Content-MD5 back).
 		uploadOption := &operation.UploadOption{
 			Filename:          filename,
 			Cipher:            wfs.option.Cipher,
 			IsInputCompressed: false,
 			MimeType:          "",
 			PairMap:           nil,
+			WantMd5:           true,
 		}
 		genFileUrlFn := func(host, fileId string) string {
 			fileUrl := fmt.Sprintf("http://%s/%s", host, fileId)
diff --git a/weed/operation/upload_content.go b/weed/operation/upload_content.go
index 1920478b4..075087ee0 100644
--- a/weed/operation/upload_content.go
+++ b/weed/operation/upload_content.go
@@ -3,6 +3,8 @@ package operation
 import (
 	"bytes"
 	"context"
+	"crypto/md5"
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -39,6 +41,7 @@ type UploadOption struct {
 	Jwt               security.EncodedJwt
 	RetryForever      bool
 	Md5               string
+	WantMd5           bool // compute Content-MD5 from the data when Md5 is unset and the upload is not ciphered
 	BytesBuffer       *bytes.Buffer
 	SourceUrl         string // optional: for logging when reading from a remote source
 	MaxAttempts       int    // <=0 uses the default
@@ -196,6 +199,14 @@ func (uploader *Uploader) UploadWithRetry(filerClient filer_pb.FilerClient, assi
 		assignRequest.ExpectedDataSize = uint64(len(data))
 	}
 
+	// Hash the buffer we already hold so the server echoes Content-MD5 back as
+	// the chunk ETag (std-base64 of the raw digest, the form ParseUpload
+	// verifies). Never under cipher: the server sees only ciphertext.
+	if uploadOption.WantMd5 && uploadOption.Md5 == "" && !uploadOption.Cipher {
+		digest := md5.Sum(data)
+		uploadOption.Md5 = base64.StdEncoding.EncodeToString(digest[:])
+	}
+
 	fileId, uploadResult, err = uploader.uploadWithRetryData(func() (fileId string, host string, auth security.EncodedJwt, err error) {
 		// grpc assign volume
 		if grpcAssignErr := filerClient.WithFilerClient(false, func(client filer_pb.SeaweedFilerClient) error {