diff --git a/cmd/basecli/commands/cmds.go b/cmd/basecli/commands/cmds.go
index e5fff36342..4c5a90640e 100644
--- a/cmd/basecli/commands/cmds.go
+++ b/cmd/basecli/commands/cmds.go
@@ -44,7 +44,7 @@ func init() {
 	flags.String(FlagAmount, "", "Coins to send in the format <amt><coin>,<amt><coin>...")
 	flags.String(FlagFee, "0mycoin", "Coins for the transaction fee of the format <amt><coin>")
 	flags.Uint64(FlagGas, 0, "Amount of gas for this transaction")
-	flags.Int64(FlagExpires, 0, "Block height at which this tx expires")
+	flags.Uint64(FlagExpires, 0, "Block height at which this tx expires")
 	flags.Int(FlagSequence, -1, "Sequence number for this transaction")
 }
 
@@ -86,10 +86,11 @@ func doSendTx(cmd *cobra.Command, args []string) error {
 // WrapChainTx will wrap the tx with a ChainTx from the standard flags
 func WrapChainTx(tx basecoin.Tx) (res basecoin.Tx, err error) {
 	expires := viper.GetInt64(FlagExpires)
-	if expires < 0 {
-		return res, errors.New("expires must be >= 0")
+	chain := commands.GetChainID()
+	if chain == "" {
+		return res, errors.New("No chain-id provided")
 	}
-	res = base.NewChainTx(commands.GetChainID(), uint64(expires), tx)
+	res = base.NewChainTx(chain, uint64(expires), tx)
 	return res, nil
 }
 
diff --git a/modules/base/chain.go b/modules/base/chain.go
index 8161f8802e..65513679de 100644
--- a/modules/base/chain.go
+++ b/modules/base/chain.go
@@ -26,7 +26,7 @@ var _ stack.Middleware = Chain{}
 
 // CheckTx makes sure we are on the proper chain - fulfills Middlware interface
 func (c Chain) CheckTx(ctx basecoin.Context, store state.KVStore, tx basecoin.Tx, next basecoin.Checker) (res basecoin.Result, err error) {
-	stx, err := c.checkChain(ctx.ChainID(), ctx.BlockHeight(), tx)
+	stx, err := c.checkChainTx(ctx.ChainID(), ctx.BlockHeight(), tx)
 	if err != nil {
 		return res, err
 	}
@@ -35,15 +35,16 @@ func (c Chain) CheckTx(ctx basecoin.Context, store state.KVStore, tx basecoin.Tx
 
 // DeliverTx makes sure we are on the proper chain - fulfills Middlware interface
 func (c Chain) DeliverTx(ctx basecoin.Context, store state.KVStore, tx basecoin.Tx, next basecoin.Deliver) (res basecoin.Result, err error) {
-	stx, err := c.checkChain(ctx.ChainID(), ctx.BlockHeight(), tx)
+	stx, err := c.checkChainTx(ctx.ChainID(), ctx.BlockHeight(), tx)
 	if err != nil {
 		return res, err
 	}
 	return next.DeliverTx(ctx, store, stx)
 }
 
-// checkChain makes sure the tx is a Chain Tx and is on the proper chain
-func (c Chain) checkChain(chainID string, height uint64, tx basecoin.Tx) (basecoin.Tx, error) {
+// checkChainTx makes sure the tx is a Chain Tx, it is on the proper chain,
+// and it has not expired.
+func (c Chain) checkChainTx(chainID string, height uint64, tx basecoin.Tx) (basecoin.Tx, error) {
 	// make sure it is a chaintx
 	ctx, ok := tx.Unwrap().(ChainTx)
 	if !ok {
diff --git a/modules/base/tx.go b/modules/base/tx.go
index 819811ef6c..fd66fad884 100644
--- a/modules/base/tx.go
+++ b/modules/base/tx.go
@@ -56,8 +56,10 @@ func (mt MultiTx) ValidateBasic() error {
 
 // ChainTx locks this tx to one chainTx, wrap with this before signing
 type ChainTx struct {
-	ChainID   string      `json:"chain_id"`   // name of chain, must be [A-Za-z0-9_-]+
-	ExpiresAt uint64      `json:"expires_at"` // block height at which it is no longer valid
+	// name of chain, must be [A-Za-z0-9_-]+
+	ChainID string `json:"chain_id"`
+	// block height at which it is no longer valid, 0 means no expiration
+	ExpiresAt uint64      `json:"expires_at"`
 	Tx        basecoin.Tx `json:"tx"`
 }
 
@@ -67,7 +69,8 @@ var (
 	chainPattern = regexp.MustCompile("^[A-Za-z0-9_-]+$")
 )
 
-//nolint - TxInner Functions
+// NewChainTx wraps a particular tx with the ChainTx wrapper,
+// to enforce chain and height
 func NewChainTx(chainID string, expires uint64, tx basecoin.Tx) basecoin.Tx {
 	c := ChainTx{
 		ChainID:   chainID,
@@ -76,6 +79,8 @@ func NewChainTx(chainID string, expires uint64, tx basecoin.Tx) basecoin.Tx {
 	}
 	return c.Wrap()
 }
+
+//nolint - TxInner Functions
 func (c ChainTx) Wrap() basecoin.Tx {
 	return basecoin.Tx{c}
 }