diff --git a/common/crypto/chunk.go b/common/crypto/chunk.go
index 0fc89db83..f284ef19d 100644
--- a/common/crypto/chunk.go
+++ b/common/crypto/chunk.go
@@ -73,7 +73,7 @@ func (r *ChunkStreamReader) readSize() (uint16, error) {
 			return 0, err
 		}
 	}
-	common.Must2(r.leftOver.Read(r.buffer))
+	common.Must2(io.ReadFull(&r.leftOver, r.buffer))
 	return r.sizeDecoder.Decode(r.buffer)
 }