diff --git a/cmd/barak/main.go b/cmd/barak/main.go
index ca64e4176..8c54fddf3 100644
--- a/cmd/barak/main.go
+++ b/cmd/barak/main.go
@@ -50,7 +50,9 @@ func main() {
 	fmt.Printf("New Barak Process (PID: %d)\n", os.Getpid())
 
 	// Apply bare tendermint/* configuration.
-	cfg.ApplyConfig(cfg.MapConfig(map[string]interface{}{"log_level": "info"}))
+	config := cfg.NewMapConfig(nil)
+	config.Set("log_level", "info")
+	cfg.ApplyConfig(config)
 
 	// Read options
 	optionsFile := parseFlags()
diff --git a/cmd/debora/main.go b/cmd/debora/main.go
index 45a1b0c52..402ea520c 100644
--- a/cmd/debora/main.go
+++ b/cmd/debora/main.go
@@ -35,7 +35,9 @@ func main() {
 	fmt.Printf("New Debora Process (PID: %d)\n", os.Getpid())
 
 	// Apply bare tendermint/* configuration.
-	cfg.ApplyConfig(cfg.MapConfig(map[string]interface{}{"log_level": "notice"}))
+	config := cfg.NewMapConfig(nil)
+	config.Set("log_level", "notice")
+	cfg.ApplyConfig(config)
 
 	rootDir := os.Getenv("DEBROOT")
 	if rootDir == "" {
diff --git a/config/config.go b/config/config.go
index 43963e25a..c9becc984 100644
--- a/config/config.go
+++ b/config/config.go
@@ -1,8 +1,11 @@
 package config
 
 import (
+	"github.com/tendermint/tendermint/Godeps/_workspace/src/github.com/naoina/toml"
 	"sync"
 	"time"
+
+	. "github.com/tendermint/tendermint/common"
 )
 
 type Config interface {
@@ -19,28 +22,66 @@ type Config interface {
 	Set(key string, value interface{})
 }
 
-type MapConfig map[string]interface{}
+type MapConfig struct {
+	required map[string]struct{} // blows up if trying to use before setting.
+	data     map[string]interface{}
+}
+
+func ReadMapConfigFromFile(filePath string) (MapConfig, error) {
+	var configData = make(map[string]interface{})
+	fileBytes := MustReadFile(filePath)
+	err := toml.Unmarshal(fileBytes, configData)
+	if err != nil {
+		return MapConfig{}, err
+	}
+	return NewMapConfig(configData), nil
+}
+
+func NewMapConfig(data map[string]interface{}) MapConfig {
+	if data == nil {
+		data = make(map[string]interface{})
+	}
+	return MapConfig{
+		required: make(map[string]struct{}),
+		data:     data,
+	}
+}
 
-func (cfg MapConfig) Get(key string) interface{}    { return cfg[key] }
-func (cfg MapConfig) GetBool(key string) bool       { return cfg[key].(bool) }
-func (cfg MapConfig) GetFloat64(key string) float64 { return cfg[key].(float64) }
-func (cfg MapConfig) GetInt(key string) int         { return cfg[key].(int) }
-func (cfg MapConfig) GetString(key string) string   { return cfg[key].(string) }
+func (cfg MapConfig) Get(key string) interface{} {
+	if _, ok := cfg.required[key]; ok {
+		PanicSanity(Fmt("config key %v is required but was not set.", key))
+	}
+	return cfg.data[key]
+}
+func (cfg MapConfig) GetBool(key string) bool       { return cfg.Get(key).(bool) }
+func (cfg MapConfig) GetFloat64(key string) float64 { return cfg.Get(key).(float64) }
+func (cfg MapConfig) GetInt(key string) int         { return cfg.Get(key).(int) }
+func (cfg MapConfig) GetString(key string) string   { return cfg.Get(key).(string) }
 func (cfg MapConfig) GetStringMap(key string) map[string]interface{} {
-	return cfg[key].(map[string]interface{})
+	return cfg.Get(key).(map[string]interface{})
 }
 func (cfg MapConfig) GetStringMapString(key string) map[string]string {
-	return cfg[key].(map[string]string)
+	return cfg.Get(key).(map[string]string)
+}
+func (cfg MapConfig) GetStringSlice(key string) []string { return cfg.Get(key).([]string) }
+func (cfg MapConfig) GetTime(key string) time.Time       { return cfg.Get(key).(time.Time) }
+func (cfg MapConfig) IsSet(key string) bool              { _, ok := cfg.data[key]; return ok }
+func (cfg MapConfig) Set(key string, value interface{}) {
+	delete(cfg.required, key)
+	cfg.data[key] = value
 }
-func (cfg MapConfig) GetStringSlice(key string) []string { return cfg[key].([]string) }
-func (cfg MapConfig) GetTime(key string) time.Time       { return cfg[key].(time.Time) }
-func (cfg MapConfig) IsSet(key string) bool              { _, ok := cfg[key]; return ok }
-func (cfg MapConfig) Set(key string, value interface{})  { cfg[key] = value }
 func (cfg MapConfig) SetDefault(key string, value interface{}) {
+	delete(cfg.required, key)
+	if cfg.IsSet(key) {
+		return
+	}
+	cfg.data[key] = value
+}
+func (cfg MapConfig) SetRequired(key string) {
 	if cfg.IsSet(key) {
 		return
 	}
-	cfg[key] = value
+	cfg.required[key] = struct{}{}
 }
 
 //--------------------------------------------------------------------------------
diff --git a/config/tendermint/config.go b/config/tendermint/config.go
index e8abcebbb..e18f3c83f 100644
--- a/config/tendermint/config.go
+++ b/config/tendermint/config.go
@@ -1,7 +1,6 @@
 package tendermint
 
 import (
-	"github.com/tendermint/tendermint/Godeps/_workspace/src/github.com/naoina/toml"
 	"os"
 	"path"
 	"strings"
@@ -38,10 +37,8 @@ func GetConfig(rootDir string) cfg.Config {
 	rootDir = getTMRoot(rootDir)
 	initTMRoot(rootDir)
 
-	var mapConfig = cfg.MapConfig(make(map[string]interface{}))
 	configFilePath := path.Join(rootDir, "config.toml")
-	configFileBytes := MustReadFile(configFilePath)
-	err := toml.Unmarshal(configFileBytes, mapConfig)
+	mapConfig, err := cfg.ReadMapConfigFromFile(configFilePath)
 	if err != nil {
 		Exit(Fmt("Could not read config: %v", err))
 	}
@@ -53,7 +50,7 @@ func GetConfig(rootDir string) cfg.Config {
 	if mapConfig.IsSet("revision_file") {
 		Exit("Cannot set 'revision_file' via config.toml. It must match what's in the Makefile")
 	}
-	mapConfig.SetDefault("chain_id", "tendermint_testnet_11.c") // TODO ALSO UPDATE GENESIS BELOW!!!
+	mapConfig.SetRequired("chain_id") // blows up if you try to use it before setting.
 	mapConfig.SetDefault("genesis_file", rootDir+"/genesis.json")
 	mapConfig.SetDefault("moniker", "anonymous")
 	mapConfig.SetDefault("node_laddr", "0.0.0.0:46656")
@@ -73,12 +70,6 @@ func GetConfig(rootDir string) cfg.Config {
 	return mapConfig
 }
 
-func ensureDefault(mapConfig cfg.MapConfig, key string, value interface{}) {
-	if !mapConfig.IsSet(key) {
-		mapConfig[key] = value
-	}
-}
-
 var defaultConfigTmpl = `# This is a TOML config file.
 # For more information, see https://github.com/toml-lang/toml
 
diff --git a/config/tendermint_test/config.go b/config/tendermint_test/config.go
index 79a42e495..9e530a71d 100644
--- a/config/tendermint_test/config.go
+++ b/config/tendermint_test/config.go
@@ -3,7 +3,6 @@
 package tendermint_test
 
 import (
-	"github.com/tendermint/tendermint/Godeps/_workspace/src/github.com/naoina/toml"
 	"os"
 	"path"
 	"strings"
@@ -47,10 +46,8 @@ func GetConfig(rootDir string) cfg.Config {
 	rootDir = getTMRoot(rootDir)
 	initTMRoot(rootDir)
 
-	var mapConfig = cfg.MapConfig(make(map[string]interface{}))
 	configFilePath := path.Join(rootDir, "config.toml")
-	configFileBytes := MustReadFile(configFilePath)
-	err := toml.Unmarshal(configFileBytes, mapConfig)
+	mapConfig, err := cfg.ReadMapConfigFromFile(configFilePath)
 	if err != nil {
 		Exit(Fmt("Could not read config: %v", err))
 	}
@@ -78,12 +75,6 @@ func GetConfig(rootDir string) cfg.Config {
 	return mapConfig
 }
 
-func ensureDefault(mapConfig cfg.MapConfig, key string, value interface{}) {
-	if !mapConfig.IsSet(key) {
-		mapConfig[key] = value
-	}
-}
-
 var defaultConfigTmpl = `# This is a TOML config file.
 # For more information, see https://github.com/toml-lang/toml
 
diff --git a/node/node.go b/node/node.go
index 1ca41b935..75c35da2f 100644
--- a/node/node.go
+++ b/node/node.go
@@ -2,6 +2,7 @@ package node
 
 import (
 	"bytes"
+	"io/ioutil"
 	"math/rand"
 	"net"
 	"net/http"
@@ -297,6 +298,16 @@ func RunNode() {
 			if FileExists(genDocFile) {
 				break
 			}
+			jsonBlob, err := ioutil.ReadFile(genDocFile)
+			if err != nil {
+				Exit(Fmt("Couldn't read GenesisDoc file: %v", err))
+			}
+			genDoc := stypes.GenesisDocFromJSON(jsonBlob)
+			if genDoc.ChainID == "" {
+				PanicSanity(Fmt("Genesis doc %v must include non-empty chain_id", genDocFile))
+			}
+			config.Set("chain_id", genDoc.ChainID)
+			config.Set("genesis_doc", genDoc)
 		}
 	}