diff --git a/consensus/invalid_test.go b/consensus/invalid_test.go
new file mode 100644
index 000000000..1ae0a69ec
--- /dev/null
+++ b/consensus/invalid_test.go
@@ -0,0 +1,94 @@
+package consensus
+
+import (
+	"testing"
+
+	"github.com/tendermint/tendermint/libs/bytes"
+	"github.com/tendermint/tendermint/libs/log"
+	tmrand "github.com/tendermint/tendermint/libs/rand"
+	"github.com/tendermint/tendermint/p2p"
+	"github.com/tendermint/tendermint/types"
+)
+
+//----------------------------------------------
+// byzantine failures
+
+// one byz val sends a precommit for a random block at each height
+// Ensure a testnet makes blocks
+func TestReactorInvalidPrecommit(t *testing.T) {
+	N := 4
+	css, cleanup := randConsensusNet(N, "consensus_reactor_test", newMockTickerFunc(true), newCounter)
+	defer cleanup()
+
+	for i := 0; i < 4; i++ {
+		ticker := NewTimeoutTicker()
+		ticker.SetLogger(css[i].Logger)
+		css[i].SetTimeoutTicker(ticker)
+
+	}
+
+	reactors, blocksSubs, eventBuses := startConsensusNet(t, css, N)
+
+	// this val sends a random precommit at each height
+	byzValIdx := 0
+	byzVal := css[byzValIdx]
+	byzR := reactors[byzValIdx]
+
+	// update the doPrevote function to just send a valid precommit for a random block
+	// and otherwise disable the priv validator
+	byzVal.mtx.Lock()
+	pv := byzVal.privValidator
+	byzVal.doPrevote = func(height int64, round int) {
+		invalidDoPrevoteFunc(t, height, round, byzVal, byzR.Switch, pv)
+	}
+	byzVal.mtx.Unlock()
+	defer stopConsensusNet(log.TestingLogger(), reactors, eventBuses)
+
+	// wait for a bunch of blocks
+	// TODO: make this tighter by ensuring the halt happens by block 2
+	for i := 0; i < 10; i++ {
+		timeoutWaitGroup(t, N, func(j int) {
+			<-blocksSubs[j].Out()
+		}, css)
+	}
+}
+
+func invalidDoPrevoteFunc(t *testing.T, height int64, round int, cs *State, sw *p2p.Switch, pv types.PrivValidator) {
+	// routine to:
+	// - precommit for a random block
+	// - send precommit to all peers
+	// - disable privValidator (so we don't do normal precommits)
+	go func() {
+		cs.mtx.Lock()
+		cs.privValidator = pv
+		pubKey, err := cs.privValidator.GetPubKey()
+		if err != nil {
+			panic(err)
+		}
+		addr := pubKey.Address()
+		valIndex, _ := cs.Validators.GetByAddress(addr)
+
+		// precommit a random block
+		blockHash := bytes.HexBytes(tmrand.Bytes(32))
+		precommit := &types.Vote{
+			ValidatorAddress: addr,
+			ValidatorIndex:   valIndex,
+			Height:           cs.Height,
+			Round:            cs.Round,
+			Timestamp:        cs.voteTime(),
+			Type:             types.PrecommitType,
+			BlockID: types.BlockID{
+				Hash:        blockHash,
+				PartsHeader: types.PartSetHeader{Total: 1, Hash: tmrand.Bytes(32)}},
+		}
+		cs.privValidator.SignVote(cs.state.ChainID, precommit)
+		cs.privValidator = nil // disable priv val so we don't do normal votes
+		cs.mtx.Unlock()
+
+		peers := sw.Peers().List()
+		for _, peer := range peers {
+			cs.Logger.Info("Sending bad vote", "block", blockHash, "peer", peer)
+			peer.Send(VoteChannel, cdc.MustMarshalBinaryBare(&VoteMessage{precommit}))
+		}
+	}()
+}
diff --git a/types/vote_set.go b/types/vote_set.go
index 82698fe51..6ff6e02a5 100644
--- a/types/vote_set.go
+++ b/types/vote_set.go
@@ -547,9 +547,11 @@ func (voteSet *VoteSet) sumTotalFrac() (int64, int64, float64) {
 //--------------------------------------------------------------------------------
 // Commit
 
-// MakeCommit constructs a Commit from the VoteSet.
-// Panics if the vote type is not PrecommitType or if
-// there's no +2/3 votes for a single block.
+// MakeCommit constructs a Commit from the VoteSet. It only includes precommits
+// for the block, which has 2/3+ majority, and nil.
+//
+// Panics if the vote type is not PrecommitType or if there's no +2/3 votes for
+// a single block.
 func (voteSet *VoteSet) MakeCommit() *Commit {
 	if voteSet.signedMsgType != PrecommitType {
 		panic("Cannot MakeCommit() unless VoteSet.Type is PrecommitType")
@@ -565,7 +567,12 @@ func (voteSet *VoteSet) MakeCommit() *Commit {
 	// For every validator, get the precommit
 	commitSigs := make([]CommitSig, len(voteSet.votes))
 	for i, v := range voteSet.votes {
-		commitSigs[i] = v.CommitSig()
+		commitSig := v.CommitSig()
+		// if block ID exists but doesn't match, exclude sig
+		if commitSig.ForBlock() && !v.BlockID.Equals(*voteSet.maj23) {
+			commitSig = NewCommitSigAbsent()
+		}
+		commitSigs[i] = commitSig
 	}
 
 	return NewCommit(voteSet.GetHeight(), voteSet.GetRound(), *voteSet.maj23, commitSigs)