diff --git a/api/api_full.go b/api/api_full.go
index 6e6796476..6b3dfa6fd 100644
--- a/api/api_full.go
+++ b/api/api_full.go
@@ -41,6 +41,7 @@ type FullNode interface {
 	SyncState(context.Context) (*SyncState, error)
 	SyncSubmitBlock(ctx context.Context, blk *types.BlockMsg) error
 	SyncIncomingBlocks(ctx context.Context) (<-chan *types.BlockHeader, error)
+	SyncMarkBad(ctx context.Context, bcid cid.Cid) error
 
 	// messages
 	MpoolPending(context.Context, *types.TipSet) ([]*types.SignedMessage, error)
diff --git a/api/apistruct/struct.go b/api/apistruct/struct.go
index 7a95f318c..09e686731 100644
--- a/api/apistruct/struct.go
+++ b/api/apistruct/struct.go
@@ -58,6 +58,7 @@ type FullNodeStruct struct {
 		SyncState          func(context.Context) (*api.SyncState, error)                `perm:"read"`
 		SyncSubmitBlock    func(ctx context.Context, blk *types.BlockMsg) error         `perm:"write"`
 		SyncIncomingBlocks func(ctx context.Context) (<-chan *types.BlockHeader, error) `perm:"read"`
+		SyncMarkBad        func(ctx context.Context, bcid cid.Cid) error                `perm:"admin"`
 
 		MpoolPending     func(context.Context, *types.TipSet) ([]*types.SignedMessage, error) `perm:"read"`
 		MpoolPush        func(context.Context, *types.SignedMessage) error                    `perm:"write"`
@@ -360,6 +361,10 @@ func (c *FullNodeStruct) SyncIncomingBlocks(ctx context.Context) (<-chan *types.
 	return c.Internal.SyncIncomingBlocks(ctx)
 }
 
+func (c *FullNodeStruct) SyncMarkBad(ctx context.Context, bcid cid.Cid) error {
+	return c.Internal.SyncMarkBad(ctx, bcid)
+}
+
 func (c *FullNodeStruct) StateMinerSectors(ctx context.Context, addr address.Address, ts *types.TipSet) ([]*api.ChainSectorInfo, error) {
 	return c.Internal.StateMinerSectors(ctx, addr, ts)
 }
diff --git a/chain/sync.go b/chain/sync.go
index 19d83df27..9065bc099 100644
--- a/chain/sync.go
+++ b/chain/sync.go
@@ -1181,3 +1181,7 @@ func (syncer *Syncer) State() []SyncerState {
 	}
 	return out
 }
+
+func (syncer *Syncer) MarkBad(blk cid.Cid) {
+	syncer.bad.Add(blk)
+}
diff --git a/cli/sync.go b/cli/sync.go
index 1b051769a..d3d425967 100644
--- a/cli/sync.go
+++ b/cli/sync.go
@@ -19,6 +19,7 @@ var syncCmd = &cli.Command{
 	Subcommands: []*cli.Command{
 		syncStatusCmd,
 		syncWaitCmd,
+		syncMarkBadCmd,
 	},
 }
 
@@ -90,6 +91,30 @@ var syncWaitCmd = &cli.Command{
 	},
 }
 
+var syncMarkBadCmd = &cli.Command{
+	Name:  "mark-bad",
+	Usage: "Mark the given block as bad, will prevent syncing to a chain that contains it",
+	Action: func(cctx *cli.Context) error {
+		napi, closer, err := GetFullNodeAPI(cctx)
+		if err != nil {
+			return err
+		}
+		defer closer()
+		ctx := ReqContext(cctx)
+
+		if !cctx.Args().Present() {
+			return fmt.Errorf("must specify block cid to mark")
+		}
+
+		bcid, err := cid.Decode(cctx.Args().First())
+		if err != nil {
+			return fmt.Errorf("failed to decode input as a cid: %s", err)
+		}
+
+		return napi.SyncMarkBad(ctx, bcid)
+	},
+}
+
 func SyncWait(ctx context.Context, napi api.FullNode) error {
 	for {
 		state, err := napi.SyncState(ctx)
diff --git a/go.mod b/go.mod
index 3283f456b..e9e85962d 100644
--- a/go.mod
+++ b/go.mod
@@ -83,6 +83,7 @@ require (
 	github.com/onsi/gomega v1.6.0 // indirect
 	github.com/opentracing/opentracing-go v1.1.0
 	github.com/polydawn/refmt v0.0.0-20190809202753-05966cbd336a
+	github.com/prometheus/common v0.2.0
 	github.com/stretchr/testify v1.4.0
 	github.com/whyrusleeping/bencher v0.0.0-20190829221104-bb6607aa8bba
 	github.com/whyrusleeping/cbor-gen v0.0.0-20191216205031-b047b6acb3c0
diff --git a/go.sum b/go.sum
index 34d5667dc..2a5f3c8fa 100644
--- a/go.sum
+++ b/go.sum
@@ -23,7 +23,9 @@ github.com/Stebalien/go-bitfield v0.0.1/go.mod h1:GNjFpasyUVkHMsfEOk8EFLJ9syQ6SI
 github.com/aead/siphash v1.0.1/go.mod h1:Nywa3cDsYNNK3gaciGTWPwHt0wlpNV15vwmswBAUSII=
 github.com/akavel/rsrc v0.8.0 h1:zjWn7ukO9Kc5Q62DOJCcxGpXC18RawVtYAGdz2aLlfw=
 github.com/akavel/rsrc v0.8.0/go.mod h1:uLoCtb9J+EyAqh+26kdrTgmzRBFPGOolLWKpdxkKq+c=
+github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc h1:cAKDfWh5VpdgMhJosfJnn5/FoN2SRZ4p7fJNX58YPaU=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
+github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf h1:qet1QNfXsQxTZqLG4oE62mJzwPIB8+Tee4RNCL9ulrY=
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
 github.com/apache/thrift v0.12.0 h1:pODnxUFNcjP9UTLZGTdeh+j16A8lJbRvD3rOtrk/7bs=
 github.com/apache/thrift v0.12.0/go.mod h1:cp2SuWMxlEZw2r+iP2GNCdIi4C1qmUzdZFSVb+bacwQ=
@@ -293,6 +295,7 @@ github.com/kisielk/errcheck v1.1.0/go.mod h1:EZBBE59ingxPouuu3KfxchcWSUPOHkagtvW
 github.com/kisielk/errcheck v1.2.0/go.mod h1:/BMXB+zMLi60iA8Vv6Ksmxu/1UDYcXs4uQLJ+jE2L00=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
 github.com/kkdai/bstream v0.0.0-20161212061736-f391b8402d23/go.mod h1:J+Gs4SYgM6CZQHDETBtE9HaSEkGmuNXF86RwHhHUvq4=
+github.com/konsorten/go-windows-terminal-sequences v1.0.1 h1:mweAR1A6xJ3oS2pRaGiHgQ4OO8tzTaLawm8vnODuwDk=
 github.com/konsorten/go-windows-terminal-sequences v1.0.1/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/koron/go-ssdp v0.0.0-20180514024734-4a0ed625a78b/go.mod h1:5Ky9EC2xfoUKUor0Hjgi2BJhCSXJfMOFlmyYrVKGQMk=
 github.com/koron/go-ssdp v0.0.0-20191105050749-2e1c40ed0b5d h1:68u9r4wEvL3gYg2jvAOgROwZ3H+Y3hIDk4tbbmIjcYQ=
@@ -542,7 +545,6 @@ github.com/multiformats/go-multistream v0.0.1/go.mod h1:fJTiDfXJVmItycydCnNx4+wS
 github.com/multiformats/go-multistream v0.0.4/go.mod h1:fJTiDfXJVmItycydCnNx4+wSzZ5NwG2FEVAI30fiovg=
 github.com/multiformats/go-multistream v0.1.0 h1:UpO6jrsjqs46mqAK3n6wKRYFhugss9ArzbyUzU+4wkQ=
 github.com/multiformats/go-multistream v0.1.0/go.mod h1:fJTiDfXJVmItycydCnNx4+wSzZ5NwG2FEVAI30fiovg=
-github.com/multiformats/go-varint v0.0.1 h1:TR/0rdQtnNxuN2IhiB639xC3tWM4IUi7DkTBVTdGW/M=
 github.com/multiformats/go-varint v0.0.1/go.mod h1:3Ls8CIEsrijN6+B7PbrXRPxHRPuXSrVKRY101jdMZYE=
 github.com/multiformats/go-varint v0.0.2 h1:6sUvyh2YHpJCb8RZ6eYzj6iJQ4+chWYmyIHxszqlPTA=
 github.com/multiformats/go-varint v0.0.2/go.mod h1:3Ls8CIEsrijN6+B7PbrXRPxHRPuXSrVKRY101jdMZYE=
@@ -584,6 +586,7 @@ github.com/prometheus/client_golang v0.9.1/go.mod h1:7SWBe2y4D6OKWSNQJUaRYU/AaXP
 github.com/prometheus/client_golang v0.9.3-0.20190127221311-3c4408c8b829/go.mod h1:p2iRAGwDERtqlqzRXnrOVns+ignqQo//hLXqYxZYVNs=
 github.com/prometheus/client_model v0.0.0-20180712105110-5c3871d89910/go.mod h1:MbSGuTsp3dbXC40dX6PRTWyKYBIrTGTE9sqQNg2J8bo=
 github.com/prometheus/client_model v0.0.0-20190115171406-56726106282f/go.mod h1:MbSGuTsp3dbXC40dX6PRTWyKYBIrTGTE9sqQNg2J8bo=
+github.com/prometheus/common v0.2.0 h1:kUZDBDTdBVBYBj5Tmh2NZLlF60mfjA27rM34b+cVwNU=
 github.com/prometheus/common v0.2.0/go.mod h1:TNfzLD0ON7rHzMJeJkieUDPYmFC7Snx/y86RQel1bk4=
 github.com/prometheus/procfs v0.0.0-20181005140218-185b4288413d/go.mod h1:c3At6R/oaqEKCNdg8wHV1ftS6bRYblBhIjjI8uT2IGk=
 github.com/prometheus/procfs v0.0.0-20190117184657-bf6a532e95b1/go.mod h1:c3At6R/oaqEKCNdg8wHV1ftS6bRYblBhIjjI8uT2IGk=
@@ -592,6 +595,7 @@ github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFR
 github.com/russross/blackfriday v1.5.2/go.mod h1:JO/DiYxRf+HjHt06OyowR9PTA263kcR/rfWxYHBV53g=
 github.com/shirou/gopsutil v2.18.12+incompatible h1:1eaJvGomDnH74/5cF4CTmTbLHAriGFsTZppLXDX93OM=
 github.com/shirou/gopsutil v2.18.12+incompatible/go.mod h1:5b4v6he4MtMOwMlS0TUMTu2PcXUg8+E1lC7eC3UO/RA=
+github.com/sirupsen/logrus v1.2.0 h1:juTguoYk5qI21pwyTXY3B3Y5cOTH3ZUyZCg1v/mihuo=
 github.com/sirupsen/logrus v1.2.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=
 github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d/go.mod h1:OnSkiWE9lh6wB0YB77sQom3nweQdgAjqCqsofrRNTgc=
 github.com/smartystreets/assertions v1.0.0/go.mod h1:kHHU4qYBaI3q23Pp3VPrmWhuIUrLW/7eUrw0BU5VaoM=
@@ -664,11 +668,9 @@ github.com/x-cray/logrus-prefixed-formatter v0.5.2/go.mod h1:2duySbKsL6M18s5GU7V
 github.com/xordataexchange/crypt v0.0.3-0.20170626215501-b2862e3d0a77/go.mod h1:aYKd//L2LvnjZzWKhF00oedf4jCCReLcmhLdhm1A27Q=
 go.opencensus.io v0.20.1/go.mod h1:6WKK9ahsWS3RSO+PY9ZHZUfv2irvY6gN279GOPZjmmk=
 go.opencensus.io v0.21.0/go.mod h1:mSImk1erAIZhrmZN+AvHh14ztQfjbGwt4TtuofqLduU=
-go.opencensus.io v0.22.1 h1:8dP3SGL7MPB94crU3bEPplMPe83FI4EouesJUeFHv50=
 go.opencensus.io v0.22.1/go.mod h1:Ap50jQcDJrx6rB6VgeeFPtuPIf3wMRvRfrfYDO6+BmA=
 go.opencensus.io v0.22.2 h1:75k/FF0Q2YM8QYo07VPddOLBslDt1MZOdEslOHvmzAs=
 go.opencensus.io v0.22.2/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
-go.uber.org/atomic v1.4.0 h1:cxzIVoETapQEqDhQu3QfnvXAV4AlzcvUCxkVUFw3+EU=
 go.uber.org/atomic v1.4.0/go.mod h1:gD2HeocX3+yG+ygLZcrzQJaqmWj9AIm7n08wl/qW/PE=
 go.uber.org/atomic v1.5.0 h1:OI5t8sDa1Or+q8AeE+yKeB/SDYioSHAgcVljj9JIETY=
 go.uber.org/atomic v1.5.0/go.mod h1:sABNBOSYdrvTF6hTgEIbc7YasKWGhgEQZyfxyTvoXHQ=
@@ -678,7 +680,6 @@ go.uber.org/fx v1.9.0 h1:7OAz8ucp35AU8eydejpYG7QrbE8rLKzGhHbZlJi5LYY=
 go.uber.org/fx v1.9.0/go.mod h1:mFdUyAUuJ3w4jAckiKSKbldsxy1ojpAMJ+dVZg5Y0Aw=
 go.uber.org/goleak v0.10.0 h1:G3eWbSNIskeRqtsN/1uI5B+eP73y3JUuBsv9AZjehb4=
 go.uber.org/goleak v0.10.0/go.mod h1:VCZuO8V8mFPlL0F5J5GK1rtHV3DrFcQ1R8ryq7FK0aI=
-go.uber.org/multierr v1.1.0 h1:HoEmRHQPVSqub6w2z2d2EOVs2fjyFRGyofhKuyDq0QI=
 go.uber.org/multierr v1.1.0/go.mod h1:wR5kodmAFQ0UK8QlbwjlSNy0Z68gJhDJUG5sjR94q/0=
 go.uber.org/multierr v1.4.0 h1:f3WCSC2KzAcBXGATIxAB1E2XuCpNU255wNKZ505qi3E=
 go.uber.org/multierr v1.4.0/go.mod h1:VgVr7evmIr6uPjLBxg28wmKNXyqE9akIJ5XnfpiKl+4=
@@ -734,7 +735,6 @@ golang.org/x/oauth2 v0.0.0-20190226205417-e64efc72b421/go.mod h1:gOpvHmFTYa4Iltr
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6 h1:bjcUS9ztw9kFmmIxJInhon/0Is3p+EHBKNgquIzo1OI=
 golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58 h1:8gQV6CLnAEikrhgkHFbMAEhagSSnXWGV915qUMm9mrU=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -797,6 +797,7 @@ google.golang.org/genproto v0.0.0-20190425155659-357c62f0e4bb/go.mod h1:VzzqZJRn
 google.golang.org/grpc v1.17.0/go.mod h1:6QZJwpn2B+Zp71q/5VxRsJ6NXXVCE5NRUHRo+f3cWCs=
 google.golang.org/grpc v1.19.0/go.mod h1:mqu4LbDTu4XGKhr4mRzUsmM4RtVoemTSY81AxZiDr8c=
 google.golang.org/grpc v1.20.1/go.mod h1:10oTOabMzJvdu6/UiuZezV6QK5dSlG84ov/aaiqXj38=
+gopkg.in/alecthomas/kingpin.v2 v2.2.6 h1:jMFz6MfLP0/4fUyZle81rXUoxOBFi19VUFKVDOQfozc=
 gopkg.in/alecthomas/kingpin.v2 v2.2.6/go.mod h1:FMv+mEhP44yOT+4EoQTLFTRgOQ1FBLkstjWtayDeSgw=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
diff --git a/node/impl/full/sync.go b/node/impl/full/sync.go
index 0ebdad536..250837ab3 100644
--- a/node/impl/full/sync.go
+++ b/node/impl/full/sync.go
@@ -6,6 +6,8 @@ import (
 	"github.com/filecoin-project/lotus/api"
 	"github.com/filecoin-project/lotus/chain"
 	"github.com/filecoin-project/lotus/chain/types"
+	cid "github.com/ipfs/go-cid"
+	"github.com/prometheus/common/log"
 
 	pubsub "github.com/libp2p/go-libp2p-pubsub"
 	"go.uber.org/fx"
@@ -80,3 +82,9 @@ func (a *SyncAPI) SyncSubmitBlock(ctx context.Context, blk *types.BlockMsg) erro
 func (a *SyncAPI) SyncIncomingBlocks(ctx context.Context) (<-chan *types.BlockHeader, error) {
 	return a.Syncer.IncomingBlocks(ctx)
 }
+
+func (a *SyncAPI) SyncMarkBad(ctx context.Context, bcid cid.Cid) error {
+	log.Warnf("Marking block %s as bad", bcid)
+	a.Syncer.MarkBad(bcid)
+	return nil
+}