diff --git a/chain/sync.go b/chain/sync.go
index e594749e9..b65341825 100644
--- a/chain/sync.go
+++ b/chain/sync.go
@@ -941,6 +941,12 @@ func (syncer *Syncer) syncFork(ctx context.Context, from *types.TipSet, to *type
 	}
 
 	for cur := 0; cur < len(tips); {
+		if nts.Height() == 0 {
+			if !syncer.Genesis.Equals(nts) {
+				return nil, xerrors.Errorf("somehow synced chain that linked back to a different genesis (bad genesis: %s)", nts.Key())
+			}
+			return nil, xerrors.Errorf("synced chain forked at genesis, refusing to sync")
+		}
 
 		if nts.Equals(tips[cur]) {
 			return tips[:cur+1], nil
diff --git a/chain/types/tipset.go b/chain/types/tipset.go
index 1ed15289e..e8d830bc5 100644
--- a/chain/types/tipset.go
+++ b/chain/types/tipset.go
@@ -10,6 +10,7 @@ import (
 	"github.com/ipfs/go-cid"
 	logging "github.com/ipfs/go-log"
 	cbg "github.com/whyrusleeping/cbor-gen"
+	"golang.org/x/xerrors"
 )
 
 var log = logging.Logger("types")
@@ -95,6 +96,10 @@ func tipsetSortFunc(blks []*BlockHeader) func(i, j int) bool {
 }
 
 func NewTipSet(blks []*BlockHeader) (*TipSet, error) {
+	if len(blks) == 0 {
+		return nil, xerrors.Errorf("NewTipSet called with zero length array of blocks")
+	}
+
 	sort.Slice(blks, tipsetSortFunc(blks))
 
 	var ts TipSet