diff --git a/common/buf/reader.go b/common/buf/reader.go
index fce13c9ba..cade2a787 100644
--- a/common/buf/reader.go
+++ b/common/buf/reader.go
@@ -73,10 +73,10 @@ func (r *bufferToBytesReader) writeToInternal(writer io.Writer) (int64, error) {
 	mbWriter := NewWriter(writer)
 	totalBytes := int64(0)
 	if r.leftOver != nil {
+		totalBytes += int64(r.leftOver.Len())
 		if err := mbWriter.Write(r.leftOver); err != nil {
 			return 0, err
 		}
-		totalBytes += int64(r.leftOver.Len())
 	}
 
 	for {