diff --git a/weed/filer/stream.go b/weed/filer/stream.go
index 2ea8ce493..3859f9a67 100644
--- a/weed/filer/stream.go
+++ b/weed/filer/stream.go
@@ -99,6 +99,7 @@ type ChunkStreamReader struct {
 }
 
 var _ = io.ReadSeeker(&ChunkStreamReader{})
+var _ = io.ReaderAt(&ChunkStreamReader{})
 
 func doNewChunkStreamReader(lookupFileIdFn wdclient.LookupFileIdFunctionType, chunks []*filer_pb.FileChunk) *ChunkStreamReader {
 
@@ -135,6 +136,14 @@ func NewChunkStreamReader(filerClient filer_pb.FilerClient, chunks []*filer_pb.F
 	return doNewChunkStreamReader(lookupFileIdFn, chunks)
 }
 
+func (c *ChunkStreamReader) ReadAt(p []byte, off int64) (n int, err error) {
+	_, err = c.Seek(off, io.SeekStart)
+	if err != nil {
+		return
+	}
+	return c.Read(p)
+}
+
 func (c *ChunkStreamReader) Read(p []byte) (n int, err error) {
 	for n < len(p) {
 		if c.isBufferEmpty() {