diff --git a/.circleci/config.yml b/.circleci/config.yml
index cbbc9514a..b502c8986 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -45,7 +45,7 @@ commands:
             - 'v25-2k-lotus-params'
           paths:
             - /var/tmp/filecoin-proof-parameters/
-      - run:  ./lotus fetch-params --proving-params 2048
+      - run:  ./lotus fetch-params 2048
       - save_cache:
           name: Save parameters cache
           key: 'v25-2k-lotus-params'
diff --git a/chain/store/store.go b/chain/store/store.go
index 7f552313f..5a5ea5bf6 100644
--- a/chain/store/store.go
+++ b/chain/store/store.go
@@ -48,6 +48,9 @@ var log = logging.Logger("chainstore")
 
 var chainHeadKey = dstore.NewKey("head")
 
+// ReorgNotifee represents a callback that gets called upon reorgs.
+type ReorgNotifee func(rev, app []*types.TipSet) error
+
 type ChainStore struct {
 	bs bstore.Blockstore
 	ds dstore.Datastore
@@ -63,8 +66,8 @@ type ChainStore struct {
 
 	cindex *ChainIndex
 
-	reorgCh          chan<- reorg
-	headChangeNotifs []func(rev, app []*types.TipSet) error
+	reorgCh        chan<- reorg
+	reorgNotifeeCh chan ReorgNotifee
 
 	mmCache *lru.ARCCache
 	tsCache *lru.ARCCache
@@ -89,8 +92,6 @@ func NewChainStore(bs bstore.Blockstore, ds dstore.Batching, vmcalls runtime.Sys
 
 	cs.cindex = ci
 
-	cs.reorgCh = cs.reorgWorker(context.TODO())
-
 	hcnf := func(rev, app []*types.TipSet) error {
 		cs.pubLk.Lock()
 		defer cs.pubLk.Unlock()
@@ -122,7 +123,8 @@ func NewChainStore(bs bstore.Blockstore, ds dstore.Batching, vmcalls runtime.Sys
 		return nil
 	}
 
-	cs.headChangeNotifs = append(cs.headChangeNotifs, hcnf, hcmetric)
+	cs.reorgNotifeeCh = make(chan ReorgNotifee)
+	cs.reorgCh = cs.reorgWorker(context.TODO(), []ReorgNotifee{hcnf, hcmetric})
 
 	return cs
 }
@@ -211,8 +213,8 @@ func (cs *ChainStore) SubHeadChanges(ctx context.Context) chan []*api.HeadChange
 	return out
 }
 
-func (cs *ChainStore) SubscribeHeadChanges(f func(rev, app []*types.TipSet) error) {
-	cs.headChangeNotifs = append(cs.headChangeNotifs, f)
+func (cs *ChainStore) SubscribeHeadChanges(f ReorgNotifee) {
+	cs.reorgNotifeeCh <- f
 }
 
 func (cs *ChainStore) SetGenesis(b *types.BlockHeader) error {
@@ -273,13 +275,19 @@ type reorg struct {
 	new *types.TipSet
 }
 
-func (cs *ChainStore) reorgWorker(ctx context.Context) chan<- reorg {
+func (cs *ChainStore) reorgWorker(ctx context.Context, initialNotifees []ReorgNotifee) chan<- reorg {
 	out := make(chan reorg, 32)
+	notifees := make([]ReorgNotifee, len(initialNotifees))
+	copy(notifees, initialNotifees)
+
 	go func() {
 		defer log.Warn("reorgWorker quit")
 
 		for {
 			select {
+			case n := <-cs.reorgNotifeeCh:
+				notifees = append(notifees, n)
+
 			case r := <-out:
 				revert, apply, err := cs.ReorgOps(r.old, r.new)
 				if err != nil {
@@ -293,7 +301,7 @@ func (cs *ChainStore) reorgWorker(ctx context.Context) chan<- reorg {
 					apply[i], apply[opp] = apply[opp], apply[i]
 				}
 
-				for _, hcf := range cs.headChangeNotifs {
+				for _, hcf := range notifees {
 					if err := hcf(revert, apply); err != nil {
 						log.Error("head change func errored (BAD): ", err)
 					}
diff --git a/cli/params.go b/cli/params.go
index b0594b641..05c0a4cda 100644
--- a/cli/params.go
+++ b/cli/params.go
@@ -10,18 +10,16 @@ import (
 )
 
 var fetchParamCmd = &cli.Command{
-	Name:  "fetch-params",
-	Usage: "Fetch proving parameters",
-	Flags: []cli.Flag{
-		&cli.StringFlag{
-			Name:  "proving-params",
-			Usage: "download params used creating proofs for given size, i.e. 32GiB",
-		},
-	},
+	Name:      "fetch-params",
+	Usage:     "Fetch proving parameters",
+	ArgsUsage: "[sectorSize]",
 	Action: func(cctx *cli.Context) error {
-		sectorSizeInt, err := units.RAMInBytes(cctx.String("proving-params"))
+		if !cctx.Args().Present() {
+			return xerrors.Errorf("must pass sector size to fetch params for (specify as \"32GiB\", for instance)")
+		}
+		sectorSizeInt, err := units.RAMInBytes(cctx.Args().First())
 		if err != nil {
-			return err
+			return xerrors.Errorf("error parsing sector size (specify as \"32GiB\", for instance): %w", err)
 		}
 		sectorSize := uint64(sectorSizeInt)
 
diff --git a/documentation/en/local-dev-net.md b/documentation/en/local-dev-net.md
index 0b352fe8a..e11d9b358 100644
--- a/documentation/en/local-dev-net.md
+++ b/documentation/en/local-dev-net.md
@@ -8,7 +8,7 @@ make 2k
 
 Download the 2048 byte parameters:
 ```sh
-./lotus fetch-params --proving-params 2048
+./lotus fetch-params 2048
 ```
 
 Pre-seal some sectors: