diff --git a/weed/s3api/filer_multipart.go b/weed/s3api/filer_multipart.go
index fefddf4b2..cbae59fae 100644
--- a/weed/s3api/filer_multipart.go
+++ b/weed/s3api/filer_multipart.go
@@ -99,10 +99,13 @@ func (s3a *S3ApiServer) completeMultipartUpload(input *s3.CompleteMultipartUploa
 
 	for _, entry := range entries {
 		if strings.HasSuffix(entry.Name, ".part") && !entry.IsDirectory {
-			partETag, found := findByPartNumber(entry.Name, completedParts)
+			partETag, isFirstPart, found := findByPartNumber(entry.Name, completedParts)
 			if !found {
 				continue
 			}
+			if isFirstPart {
+				mime = entry.GetAttributes().Mime
+			}
 			entryETag := hex.EncodeToString(entry.Attributes.GetMd5())
 			if partETag != "" && len(partETag) == 32 && entryETag != "" && entryETag != partETag {
 				glog.Errorf("completeMultipartUpload %s ETag mismatch chunk: %s part: %s", entry.Name, entryETag, partETag)
@@ -176,7 +179,7 @@ func (s3a *S3ApiServer) completeMultipartUpload(input *s3.CompleteMultipartUploa
 	return
 }
 
-func findByPartNumber(fileName string, parts []CompletedPart) (etag string, found bool) {
+func findByPartNumber(fileName string, parts []CompletedPart) (etag string, firstPart, found bool) {
 	partNumber, formatErr := strconv.Atoi(fileName[:4])
 	if formatErr != nil {
 		return
@@ -198,7 +201,7 @@ func findByPartNumber(fileName string, parts []CompletedPart) (etag string, foun
 			break
 		}
 	}
-	return parts[x+y].ETag, true
+	return parts[x+y].ETag, partNumber == 1, true
 }
 
 func (s3a *S3ApiServer) abortMultipartUpload(input *s3.AbortMultipartUploadInput) (output *s3.AbortMultipartUploadOutput, code s3err.ErrorCode) {
diff --git a/weed/s3api/s3api_object_handlers.go b/weed/s3api/s3api_object_handlers.go
index 4d0e374b2..2ba63c784 100644
--- a/weed/s3api/s3api_object_handlers.go
+++ b/weed/s3api/s3api_object_handlers.go
@@ -122,7 +122,7 @@ func (s3a *S3ApiServer) PutObjectHandler(w http.ResponseWriter, r *http.Request)
 		}
 	} else {
 		uploadUrl := s3a.toFilerUrl(bucket, object)
-		if objectContentType == "" {
+		if objectContentType == "" || objectContentType == "application/octet-stream" {
 			dataReader = mimeDetect(r, dataReader)
 		}
 
diff --git a/weed/s3api/s3api_object_multipart_handlers.go b/weed/s3api/s3api_object_multipart_handlers.go
index 07b6497ae..2784208fe 100644
--- a/weed/s3api/s3api_object_multipart_handlers.go
+++ b/weed/s3api/s3api_object_multipart_handlers.go
@@ -312,7 +312,8 @@ func (s3a *S3ApiServer) PutObjectPartHandler(w http.ResponseWriter, r *http.Requ
 	uploadUrl := fmt.Sprintf("http://%s%s/%s/%04d.part",
 		s3a.option.Filer.ToHttpAddress(), s3a.genUploadsFolder(bucket), uploadID, partID)
 
-	if partID == 1 && r.Header.Get("Content-Type") == "" {
+	contentType := r.Header.Get("Content-Type")
+	if partID == 1 && contentType == "" || contentType == "application/octet-stream" {
 		dataReader = mimeDetect(r, dataReader)
 	}