diff --git a/state/state.go b/state/state.go
index ca4e8ffd1..74504f0a3 100644
--- a/state/state.go
+++ b/state/state.go
@@ -273,8 +273,8 @@ func (s *State) SetBlockAndValidators(header *types.Header, blockPartsHeader typ
 	// Update validator accums and set state variables
 	nextValSet.IncrementAccum(1)
 
-	nextParams := applyUpdates(s.ConsensusParams,
-		abciResponses.EndBlock.ConsensusParamUpdates)
+	// NOTE: must not mutate s.ConsensusParams
+	nextParams := s.ConsensusParams.Update(abciResponses.EndBlock.ConsensusParamUpdates)
 	err := nextParams.Validate()
 	if err != nil {
 		s.logger.Error("Error updating consensus params", "err", err)
@@ -291,45 +291,6 @@ func (s *State) SetBlockAndValidators(header *types.Header, blockPartsHeader typ
 
 }
 
-// applyUpdates 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 applyUpdates(p types.ConsensusParams,
-	c *abci.ConsensusParams) types.ConsensusParams {
-
-	if c == nil {
-		return p
-	}
-	res := p
-	// we must defensively consider any structs may be nil
-	if c.BlockSize != nil {
-
-		if c.BlockSize.MaxBytes != 0 {
-			res.BlockSize.MaxBytes = int(c.BlockSize.MaxBytes)
-		}
-		if c.BlockSize.MaxTxs != 0 {
-			res.BlockSize.MaxTxs = int(c.BlockSize.MaxTxs)
-		}
-		if c.BlockSize.MaxGas != 0 {
-			res.BlockSize.MaxGas = int(c.BlockSize.MaxGas)
-		}
-	}
-	if c.TxSize != nil {
-		if c.TxSize.MaxBytes != 0 {
-			res.TxSize.MaxBytes = int(c.TxSize.MaxBytes)
-		}
-		if c.TxSize.MaxGas != 0 {
-			res.TxSize.MaxGas = int(c.TxSize.MaxGas)
-		}
-	}
-	if c.BlockGossip != nil {
-		if c.BlockGossip.BlockPartSizeBytes != 0 {
-			res.BlockGossip.BlockPartSizeBytes = int(c.BlockGossip.BlockPartSizeBytes)
-		}
-	}
-	return res
-}
-
 func (s *State) setBlockAndValidators(height int64,
 	newTxs int64, blockID types.BlockID, blockTime time.Time,
 	valSet *types.ValidatorSet,
diff --git a/types/params.go b/types/params.go
index e7c32f48f..19e86d449 100644
--- a/types/params.go
+++ b/types/params.go
@@ -3,6 +3,7 @@ package types
 import (
 	"github.com/pkg/errors"
 
+	abci "github.com/tendermint/abci/types"
 	"github.com/tendermint/tmlibs/merkle"
 )
 
@@ -20,15 +21,15 @@ type ConsensusParams struct {
 
 // BlockSize contain limits on the block size.
 type BlockSize struct {
-	MaxBytes int `json:"max_bytes"` // NOTE: must not be 0 nor greater than 100MB
-	MaxTxs   int `json:"max_txs"`
-	MaxGas   int `json:"max_gas"`
+	MaxBytes int   `json:"max_bytes"` // NOTE: must not be 0 nor greater than 100MB
+	MaxTxs   int   `json:"max_txs"`
+	MaxGas   int64 `json:"max_gas"`
 }
 
 // TxSize contain limits on the tx size.
 type TxSize struct {
-	MaxBytes int `json:"max_bytes"`
-	MaxGas   int `json:"max_gas"`
+	MaxBytes int   `json:"max_bytes"`
+	MaxGas   int64 `json:"max_gas"`
 }
 
 // BlockGossip determine consensus critical elements of how blocks are gossiped
@@ -100,3 +101,42 @@ func (params *ConsensusParams) Hash() []byte {
 		"tx_size_max_gas":              params.TxSize.MaxGas,
 	})
 }
+
+// Update returns a copy of the params with updates from the non-zero fields of p2.
+// NOTE: note: must not modify the original
+func (params ConsensusParams) Update(params2 *abci.ConsensusParams) ConsensusParams {
+	res := params // explicit copy
+
+	if params2 == nil {
+		return res
+	}
+
+	// we must defensively consider any structs may be nil
+	// XXX: it's cast city over here. It's ok because we only do int32->int
+	// but still, watch it champ.
+	if params2.BlockSize != nil {
+		if params2.BlockSize.MaxBytes > 0 {
+			res.BlockSize.MaxBytes = int(params2.BlockSize.MaxBytes)
+		}
+		if params2.BlockSize.MaxTxs > 0 {
+			res.BlockSize.MaxTxs = int(params2.BlockSize.MaxTxs)
+		}
+		if params2.BlockSize.MaxGas > 0 {
+			res.BlockSize.MaxGas = params2.BlockSize.MaxGas
+		}
+	}
+	if params2.TxSize != nil {
+		if params2.TxSize.MaxBytes > 0 {
+			res.TxSize.MaxBytes = int(params2.TxSize.MaxBytes)
+		}
+		if params2.TxSize.MaxGas > 0 {
+			res.TxSize.MaxGas = params2.TxSize.MaxGas
+		}
+	}
+	if params2.BlockGossip != nil {
+		if params2.BlockGossip.BlockPartSizeBytes > 0 {
+			res.BlockGossip.BlockPartSizeBytes = int(params2.BlockGossip.BlockPartSizeBytes)
+		}
+	}
+	return res
+}