diff --git a/blockchain/reactor_test.go b/blockchain/reactor_test.go
index e652df3fd..d3e341644 100644
--- a/blockchain/reactor_test.go
+++ b/blockchain/reactor_test.go
@@ -112,6 +112,7 @@ func makeBlock(height int64, state *sm.State) *types.Block {
 	block, _ := types.MakeBlock(height, "test_chain", makeTxs(height),
 		state.LastBlockTotalTx, new(types.Commit),
 		prevBlockID, valHash, state.AppHash,
+		state.Params.Hash(),
 		state.Params.BlockGossipParams.BlockPartSizeBytes)
 	return block
 }
diff --git a/consensus/state.go b/consensus/state.go
index 8a2692a22..1018d3704 100644
--- a/consensus/state.go
+++ b/consensus/state.go
@@ -866,7 +866,8 @@ func (cs *ConsensusState) createProposalBlock() (block *types.Block, blockParts
 	return types.MakeBlock(cs.Height, cs.state.ChainID, txs,
 		cs.state.LastBlockTotalTx, commit,
 		cs.state.LastBlockID, cs.state.Validators.Hash(),
-		cs.state.AppHash, cs.state.Params.BlockPartSizeBytes)
+		cs.state.AppHash, cs.state.Params.Hash(),
+		cs.state.Params.BlockPartSizeBytes)
 }
 
 // Enter: `timeoutPropose` after entering Propose.
diff --git a/state/execution.go b/state/execution.go
index 6f6a7ca18..fbb0954d3 100644
--- a/state/execution.go
+++ b/state/execution.go
@@ -187,7 +187,7 @@ func (s *State) ValidateBlock(block *types.Block) error {
 func (s *State) validateBlock(block *types.Block) error {
 	// Basic block validation.
 	err := block.ValidateBasic(s.ChainID, s.LastBlockHeight,
-		s.LastBlockTotalTx, s.LastBlockID, s.LastBlockTime, s.AppHash)
+		s.LastBlockTotalTx, s.LastBlockID, s.LastBlockTime, s.AppHash, s.Params.Hash())
 	if err != nil {
 		return err
 	}
diff --git a/state/execution_test.go b/state/execution_test.go
index ac5c72f26..081a71e91 100644
--- a/state/execution_test.go
+++ b/state/execution_test.go
@@ -120,7 +120,7 @@ func makeBlock(height int64, state *State) *types.Block {
 	block, _ := types.MakeBlock(height, chainID,
 		makeTxs(height), state.LastBlockTotalTx,
 		new(types.Commit), prevBlockID, valHash,
-		state.AppHash, testPartSize)
+		state.AppHash, state.Params.Hash(), testPartSize)
 	return block
 }
 
diff --git a/state/state.go b/state/state.go
index 94ca05281..d3bca4a81 100644
--- a/state/state.go
+++ b/state/state.go
@@ -269,8 +269,9 @@ func (s *State) SetBlockAndValidators(header *types.Header, blockPartsHeader typ
 
 }
 
-// applyChanges returns a new param set, overriding any
-// parameter that is non-zero in argument
+// applyChanges returns new ConsensusParams
+// whose fields are set to any non-zero fields of c.
+// If c is nil, it returns p unmodified, as it was passed in.
 func applyChanges(p types.ConsensusParams,
 	c *abci.ConsensusParams) types.ConsensusParams {
 
diff --git a/types/block.go b/types/block.go
index ff3d3811b..356776579 100644
--- a/types/block.go
+++ b/types/block.go
@@ -25,7 +25,7 @@ type Block struct {
 // TODO: Add version information to the Block struct.
 func MakeBlock(height int64, chainID string, txs []Tx,
 	totalTxs int64, commit *Commit,
-	prevBlockID BlockID, valHash, appHash []byte,
+	prevBlockID BlockID, valHash, appHash, consensusHash []byte,
 	partSize int) (*Block, *PartSet) {
 
 	newTxs := int64(len(txs))
@@ -39,6 +39,7 @@ func MakeBlock(height int64, chainID string, txs []Tx,
 			LastBlockID:    prevBlockID,
 			ValidatorsHash: valHash,
 			AppHash:        appHash, // state merkle root of txs from the previous block.
+			ConsensusHash:  consensusHash,
 		},
 		LastCommit: commit,
 		Data: &Data{
@@ -52,7 +53,7 @@ func MakeBlock(height int64, chainID string, txs []Tx,
 // ValidateBasic performs basic validation that doesn't involve state data.
 func (b *Block) ValidateBasic(chainID string, lastBlockHeight int64,
 	lastBlockTotalTx int64, lastBlockID BlockID,
-	lastBlockTime time.Time, appHash []byte) error {
+	lastBlockTime time.Time, appHash, consensusHash []byte) error {
 
 	if b.ChainID != chainID {
 		return errors.New(cmn.Fmt("Wrong Block.Header.ChainID. Expected %v, got %v", chainID, b.ChainID))
@@ -91,6 +92,13 @@ func (b *Block) ValidateBasic(chainID string, lastBlockHeight int64,
 	if !bytes.Equal(b.AppHash, appHash) {
 		return errors.New(cmn.Fmt("Wrong Block.Header.AppHash.  Expected %X, got %v", appHash, b.AppHash))
 	}
+	// TODO: make testing easier
+	if len(consensusHash) == 0 {
+		panic("food")
+	}
+	if !bytes.Equal(b.ConsensusHash, consensusHash) {
+		return errors.New(cmn.Fmt("Wrong Block.Header.ConsensusHash.  Expected %X, got %v", consensusHash, b.ConsensusHash))
+	}
 	// NOTE: the AppHash and ValidatorsHash are validated later.
 	return nil
 }
@@ -178,6 +186,7 @@ type Header struct {
 	DataHash       data.Bytes `json:"data_hash"`        // transactions
 	ValidatorsHash data.Bytes `json:"validators_hash"`  // validators for the current block
 	AppHash        data.Bytes `json:"app_hash"`         // state after txs from the previous block
+	ConsensusHash  data.Bytes `json:"consensus_hash"`   // consensus params for current block
 }
 
 // Hash returns the hash of the header.
@@ -197,6 +206,7 @@ func (h *Header) Hash() data.Bytes {
 		"Data":        h.DataHash,
 		"Validators":  h.ValidatorsHash,
 		"App":         h.AppHash,
+		"Consensus":   h.ConsensusHash,
 	})
 }
 
@@ -216,6 +226,7 @@ func (h *Header) StringIndented(indent string) string {
 %s  Data:           %v
 %s  Validators:     %v
 %s  App:            %v
+%s  Conensus:            %v
 %s}#%v`,
 		indent, h.ChainID,
 		indent, h.Height,
@@ -227,6 +238,7 @@ func (h *Header) StringIndented(indent string) string {
 		indent, h.DataHash,
 		indent, h.ValidatorsHash,
 		indent, h.AppHash,
+		indent, h.ConsensusHash,
 		indent, h.Hash())
 }
 
diff --git a/types/block_test.go b/types/block_test.go
index 25e5a76e7..a874508a4 100644
--- a/types/block_test.go
+++ b/types/block_test.go
@@ -13,6 +13,7 @@ func TestValidateBlock(t *testing.T) {
 	lastID := makeBlockID()
 	valHash := []byte("val")
 	appHash := []byte("app")
+	consensusHash := []byte("consensus-params")
 	h := int64(3)
 
 	voteSet, _, vals := randVoteSet(h-1, 1, VoteTypePrecommit,
@@ -21,33 +22,36 @@ func TestValidateBlock(t *testing.T) {
 	require.NoError(t, err)
 
 	block, _ := MakeBlock(h, "hello", txs, 10, commit,
-		lastID, valHash, appHash, 2)
+		lastID, valHash, appHash, consensusHash, 2)
 	require.NotNil(t, block)
 
 	// proper block must pass
-	err = block.ValidateBasic("hello", h-1, 10, lastID, block.Time, appHash)
+	err = block.ValidateBasic("hello", h-1, 10, lastID, block.Time, appHash, consensusHash)
 	require.NoError(t, err)
 
 	// wrong chain fails
-	err = block.ValidateBasic("other", h-1, 10, lastID, block.Time, appHash)
+	err = block.ValidateBasic("other", h-1, 10, lastID, block.Time, appHash, consensusHash)
 	require.Error(t, err)
 
 	// wrong height fails
-	err = block.ValidateBasic("hello", h+4, 10, lastID, block.Time, appHash)
+	err = block.ValidateBasic("hello", h+4, 10, lastID, block.Time, appHash, consensusHash)
 	require.Error(t, err)
 
 	// wrong total tx fails
-	err = block.ValidateBasic("hello", h-1, 15, lastID, block.Time, appHash)
+	err = block.ValidateBasic("hello", h-1, 15, lastID, block.Time, appHash, consensusHash)
 	require.Error(t, err)
 
 	// wrong blockid fails
-	err = block.ValidateBasic("hello", h-1, 10, makeBlockID(), block.Time, appHash)
+	err = block.ValidateBasic("hello", h-1, 10, makeBlockID(), block.Time, appHash, consensusHash)
 	require.Error(t, err)
 
 	// wrong app hash fails
-	err = block.ValidateBasic("hello", h-1, 10, lastID, block.Time, []byte("bad-hash"))
+	err = block.ValidateBasic("hello", h-1, 10, lastID, block.Time, []byte("bad-hash"), consensusHash)
 	require.Error(t, err)
 
+	// wrong consensus hash fails
+	err = block.ValidateBasic("hello", h-1, 10, lastID, block.Time, appHash, []byte("wrong-params"))
+	require.Error(t, err)
 }
 
 func makeBlockID() BlockID {