diff --git a/README.md b/README.md
index a15276ee2..d8550748d 100644
--- a/README.md
+++ b/README.md
@@ -19,7 +19,7 @@ All work is tracked via issues. An attempt at keeping an up-to-date view on rema
 The main branches under development at the moment are:
 * [`master`](https://github.com/filecoin-project/lotus): current testnet.
 * [`next`](https://github.com/filecoin-project/lotus/tree/next): working branch with chain-breaking changes.
-* [`interopnet`](https://github.com/filecoin-project/lotus/tree/interopnet): devnet running one of `next` commits.
+* [`ntwk-calibration`](https://github.com/filecoin-project/lotus/tree/ntwk-calibration): devnet running one of `next` commits.
 
 ## License
 
diff --git a/lib/bufbstore/buf_bstore.go b/lib/bufbstore/buf_bstore.go
index 4b430828b..4000df7d6 100644
--- a/lib/bufbstore/buf_bstore.go
+++ b/lib/bufbstore/buf_bstore.go
@@ -104,7 +104,12 @@ func (bs *BufferedBS) Get(c cid.Cid) (block.Block, error) {
 }
 
 func (bs *BufferedBS) GetSize(c cid.Cid) (int, error) {
-	panic("nyi")
+	s, err := bs.read.GetSize(c)
+	if err == bstore.ErrNotFound || s == 0 {
+		return bs.write.GetSize(c)
+	}
+
+	return s, err
 }
 
 func (bs *BufferedBS) Put(blk block.Block) error {