diff --git a/build/forks.go b/build/forks.go
new file mode 100644
index 000000000..35990bfbf
--- /dev/null
+++ b/build/forks.go
@@ -0,0 +1,3 @@
+package build
+
+const ForkCCM = 1750
diff --git a/chain/sync.go b/chain/sync.go
index b65341825..2ed52cdc5 100644
--- a/chain/sync.go
+++ b/chain/sync.go
@@ -513,6 +513,14 @@ func (syncer *Syncer) ValidateBlock(ctx context.Context, b *types.FullBlock) err
 
 		snum := types.BigDiv(mpow, types.NewInt(ssize))
 
+		// FORK START
+		if h.Height > build.ForkCCM {
+			if len(h.EPostProof.Candidates) == 0 {
+				return xerrors.Errorf("no candidates")
+			}
+		}
+		// FORK END
+
 		for _, t := range h.EPostProof.Candidates {
 			if !types.IsTicketWinner(t.Partial, ssize, snum.Uint64(), tpow) {
 				return xerrors.Errorf("miner created a block but was not a winner")
@@ -634,6 +642,13 @@ func (syncer *Syncer) VerifyElectionPoStProof(ctx context.Context, h *types.Bloc
 			SectorChallengeIndex: t.ChallengeIndex,
 		})
 	}
+	// FORK START
+	if h.Height > build.ForkCCM {
+		if len(winners) == 0 {
+			return xerrors.Errorf("no candidates")
+		}
+	}
+	// FORK END
 
 	sectorInfo, err := stmgr.GetSectorsForElectionPost(ctx, syncer.sm, baseTs, h.Miner)
 	if err != nil {
@@ -647,6 +662,7 @@ func (syncer *Syncer) VerifyElectionPoStProof(ctx context.Context, h *types.Bloc
 		return xerrors.Errorf("[TESTING] election post was invalid")
 	}
 	hvrf := sha256.Sum256(h.EPostProof.PostRand)
+
 	ok, err := sectorbuilder.VerifyElectionPost(ctx, ssize, *sectorInfo, hvrf[:], h.EPostProof.Proof, winners, h.Miner)
 	if err != nil {
 		return xerrors.Errorf("failed to verify election post: %w", err)