diff --git a/backend/electrum/blockchain.go b/backend/electrum/blockchain.go
index 6795adc..f313dcc 100644
--- a/backend/electrum/blockchain.go
+++ b/backend/electrum/blockchain.go
@@ -139,6 +139,7 @@ func NewNode(addr, port string, network utils.Network) (*Node, error) {
 	}
 
 	if port[0] == 't' {
+		// TCP
 		var p string
 		if len(port) == 1 {
 			p = defaultTCP
@@ -147,6 +148,7 @@ func NewNode(addr, port string, network utils.Network) (*Node, error) {
 		}
 		t, err = NewTCPTransport(fmt.Sprintf("%s:%s", a, p))
 	} else if port[0] == 's' {
+		// TLS
 		var p string
 		if len(port) == 1 {
 			p = defaultSSL
@@ -154,6 +156,8 @@ func NewNode(addr, port string, network utils.Network) (*Node, error) {
 			p = port[1:]
 		}
 		t, err = NewSSLTransport(fmt.Sprintf("%s:%s", a, p))
+	} else {
+		panic(fmt.Sprintf("port (%s) must start with t or s", port))
 	}
 
 	if err != nil {
diff --git a/main.go b/main.go
index 89548d5..3e798d3 100644
--- a/main.go
+++ b/main.go
@@ -9,7 +9,6 @@ import (
 	"math"
 	"net"
 	"os"
-	"strconv"
 	"strings"
 	"time"
 
@@ -37,7 +36,7 @@ var (
 	findBlock            = app.Command("find-block", "Finds the block height for a given date/time.")
 	findBlockTimestamp   = findBlock.Arg("timestamp", "Date/time to resolve. E.g. \"2006-01-02 15:04:05 MST\"").Required().String()
 	findBlockBackend     = findBlock.Flag("backend", "electrum | btcd | electrum-recorder | btcd-recorder | fixture").Default("electrum").Enum("electrum", "btcd", "electrum-recorder", "btcd-recorder", "fixture")
-	findBlockAddr        = findBlock.Flag("addr", "Backend to connect to initially. Defaults to a hardcoded node for Electrum and localhost for Btcd.").PlaceHolder("HOST:PORT").TCP()
+	findBlockAddr        = findBlock.Flag("addr", "Backend to connect to initially. Defaults to a hardcoded node for Electrum and localhost for Btcd.").PlaceHolder("HOST:PORT").String()
 	findBlockRpcUser     = findBlock.Flag("rpcuser", "RPC username").PlaceHolder("USER").String()
 	findBlockRpcPass     = findBlock.Flag("rpcpass", "RPC password").PlaceHolder("PASSWORD").String()
 	findBlockFixtureFile = findBlock.Flag("fixture-file", "Fixture file to use for recording or replaying data.").PlaceHolder("FILEPATH").String()
@@ -48,7 +47,7 @@ var (
 	computeBalanceM           = computeBalance.Flag("m", "number of signatures (quorum)").Short('m').Default("1").Int()
 	computeBalanceN           = computeBalance.Flag("n", "number of public keys").Short('n').Default("1").Int()
 	computeBalanceBackend     = computeBalance.Flag("backend", "electrum | btcd | electrum-recorder | btcd-recorder | fixture").Default("electrum").Enum("electrum", "btcd", "electrum-recorder", "btcd-recorder", "fixture")
-	computeBalanceAddr        = computeBalance.Flag("addr", "Backend to connect to initially. Defaults to a hardcoded node for Electrum and localhost for Btcd.").PlaceHolder("HOST:PORT").TCP()
+	computeBalanceAddr        = computeBalance.Flag("addr", "Backend to connect to initially. Defaults to a hardcoded node for Electrum and localhost for Btcd.").PlaceHolder("HOST:PORT").String()
 	computeBalanceRpcUser     = computeBalance.Flag("rpcuser", "RPC username").PlaceHolder("USER").String()
 	computeBalanceRpcPass     = computeBalance.Flag("rpcpass", "RPC password").PlaceHolder("PASSWORD").String()
 	computeBalanceFixtureFile = computeBalance.Flag("fixture-file", "Fixture file to use for recording or replaying data.").PlaceHolder("FILEPATH").String()
@@ -303,13 +302,14 @@ func computeBalanceBuildBackend(network Network) (backend.Backend, error) {
 	var err error
 	switch *computeBalanceBackend {
 	case "electrum":
-		addr, port := getServer(network, *computeBalanceAddr)
+		addr, port := getServer(network, "electrum", *computeBalanceAddr)
 		b, err = backend.NewElectrumBackend(addr, port, network)
 		if err != nil {
 			return nil, err
 		}
 	case "btcd":
-		b, err = backend.NewBtcdBackend((*computeBalanceAddr).String(), *computeBalanceRpcUser,
+		addr, port := getServer(network, "btcd", *computeBalanceAddr)
+		b, err = backend.NewBtcdBackend(fmt.Sprintf("%s:%s", addr, port), *computeBalanceRpcUser,
 			*computeBalanceRpcPass, network)
 		if err != nil {
 			return nil, err
@@ -318,7 +318,7 @@ func computeBalanceBuildBackend(network Network) (backend.Backend, error) {
 		if *computeBalanceFixtureFile == "" {
 			panic("electrum-recorder backend requires output --fixture-file.")
 		}
-		addr, port := getServer(network, *computeBalanceAddr)
+		addr, port := getServer(network, "electrum", *computeBalanceAddr)
 		b, err = backend.NewElectrumBackend(addr, port, network)
 		if err != nil {
 			return nil, err
@@ -328,7 +328,8 @@ func computeBalanceBuildBackend(network Network) (backend.Backend, error) {
 		if *computeBalanceFixtureFile == "" {
 			panic("btcd-recorder backend requires output --fixture-file.")
 		}
-		b, err = backend.NewBtcdBackend((*computeBalanceAddr).String(), *computeBalanceRpcUser,
+		addr, port := getServer(network, "btcd", *computeBalanceAddr)
+		b, err = backend.NewBtcdBackend(fmt.Sprintf("%s:%s", addr, port), *computeBalanceRpcUser,
 			*computeBalanceRpcPass, network)
 		if err != nil {
 			return nil, err
@@ -348,17 +349,32 @@ func computeBalanceBuildBackend(network Network) (backend.Backend, error) {
 	return b, err
 }
 
-// pick a default server for each network if none provided
-// TODO: default server should be localhost for Btcd backend.
-func getServer(network Network, addr *net.TCPAddr) (string, string) {
-	if addr != nil {
-		return addr.IP.String(), strconv.Itoa(addr.Port)
+// pick a default server for electrum or localhost for btcd
+func getServer(network Network, backend, addr string) (string, string) {
+	if addr != "" {
+		host, port, err := net.SplitHostPort(addr)
+		PanicOnError(err)
+		return host, port
 	}
-	switch network {
-	case "mainnet":
-		return "electrum.petrkr.net", "s50002"
-	case "testnet":
-		return "electrum_testnet_unlimited.criptolayer.net", "s50102"
+	switch backend {
+	case "electrum":
+		switch network {
+		case "mainnet":
+			return "electrum.petrkr.net", "s50002"
+		case "testnet":
+			return "electrum_testnet_unlimited.criptolayer.net", "s50102"
+		default:
+			panic("unreachable")
+		}
+	case "btcd":
+		switch network {
+		case "mainnet":
+			return "localhost", "8334"
+		case "testnet":
+			return "localhost", "18334"
+		default:
+			panic("unreachable")
+		}
 	default:
 		panic("unreachable")
 	}