diff --git a/datatype.go b/datatype.go
index 6933880..687d235 100644
--- a/datatype.go
+++ b/datatype.go
@@ -22,7 +22,6 @@ type cValue struct {
 	durval  time.Duration
 	boolval bool
 	strval  string
-	mapval  map[string]cValue
 	err     error
 }
 
diff --git a/envconf.go b/envconf.go
index 4697c83..d5ad713 100644
--- a/envconf.go
+++ b/envconf.go
@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"regexp"
 	"strings"
 	"time"
 	"unicode"
@@ -38,26 +39,22 @@ func NewConfig() *Config {
 		splitted := strings.SplitN(v, "=", 2)
 		if len(splitted) == 2 {
 			key := cleanKey(splitted[0])
-			keysplit := strings.Split(key, "_")
-			left := ""
-			right := ""
-
-			if len(keysplit) > 1 {
-				left = strings.Join(keysplit[:len(keysplit)-1], "_")
-				right = keysplit[len(keysplit)-1]
-			}
+			left, right, mappable := keySplit(key)
 
 			if unicode.IsLetter(getFirstRune(key)) {
-				if len(config.mapEnv[left]) == 0 {
-					config.mapEnv[left] = make(map[string]cEntry)
-				}
 				var entry cEntry
 				entry.value = splitted[1]
 				entry.dtype = TypeNone
 				entry.unset = false
 				entry.empty = false
 				config.env[key] = entry
-				config.mapEnv[left][right] = entry
+				if mappable {
+					if len(config.mapEnv[left]) == 0 {
+						config.mapEnv[left] = make(map[string]cEntry)
+					}
+
+					config.mapEnv[left][right] = entry
+				}
 			}
 		}
 	}
@@ -67,17 +64,17 @@ func NewConfig() *Config {
 // Define the type of an environment variable.
 // Variables without a defined type will be ignored by Parse.
 func (c *Config) Define(key string, dtype DataType) {
-	upper := strings.ToUpper(key)
-	entry, ok := c.env[upper]
+	key = cleanKey(key)
+	entry, ok := c.env[key]
 	if ok {
 		entry.dtype = dtype
-		c.env[upper] = entry
+		c.env[key] = entry
 	} else {
 		var entry cEntry
 		entry.dtype = dtype
 		entry.unset = true
 		entry.empty = true
-		c.env[upper] = entry
+		c.env[key] = entry
 	}
 }
 
@@ -97,8 +94,8 @@ func (c *Config) DefineMap(key string, dtype DataType) {
 // Define the type and default value of an environment variable.
 // Variables without a defined type will be ignored by Parse.
 func (c *Config) DefineDefault(key string, val string, dtype DataType) {
-	upper := strings.ToUpper(key)
-	entry, ok := c.env[upper]
+	key = cleanKey(key)
+	entry, ok := c.env[key]
 	if ok {
 		if entry.unset {
 			entry.value = val
@@ -107,7 +104,7 @@ func (c *Config) DefineDefault(key string, val string, dtype DataType) {
 		entry.empty = false
 		entry.defval = val
 		entry.hasdef = true
-		c.env[upper] = entry
+		c.env[key] = entry
 	} else {
 		var entry cEntry
 		entry.dtype = dtype
@@ -116,7 +113,7 @@ func (c *Config) DefineDefault(key string, val string, dtype DataType) {
 		entry.value = val
 		entry.defval = val
 		entry.hasdef = true
-		c.env[upper] = entry
+		c.env[key] = entry
 	}
 }
 
@@ -261,7 +258,8 @@ func (c *Config) Status() (ok bool) {
 	return
 }
 
-func cleanKey(str string) string {
+func cleanKey(key string) string {
+	expr := regexp.MustCompile("_+")
 	fn := func(r rune) rune {
 		if (r >= '0' && r <= '9') || (r >= 'A' && r <= 'Z') || r == '_' {
 			return r
@@ -269,24 +267,25 @@ func cleanKey(str string) string {
 		return -1
 	}
 
-	str = strings.Map(fn, strings.ToUpper(str))
+	key = strings.Map(fn, strings.ToUpper(key))
+	return expr.ReplaceAllString(key, "_")
+}
 
-	oldlen := len(str) + 1
-	newlen := len(str)
-	for newlen < oldlen {
-		oldlen = newlen
-		str = strings.ReplaceAll(str, "__", "_")
-		newlen = len(str)
+func keySplit(key string) (left string, right string, ok bool) {
+	key = cleanKey(key)
+	pos := strings.LastIndex(key, "_")
+	ok = false
+	if (pos+1 < len(key)) && (pos > 1) {
+		return cleanKey(key[:pos]), cleanKey(key[pos:]), true
 	}
-
-	return str
+	return
 }
 
 func (c *Config) getRaw(key string, dtype DataType) (val cValue) {
 	val.dtype = TypeNone
 	if c.parsed {
-		upper := strings.ToUpper(key)
-		entry, ok := c.env[upper]
+		key = cleanKey(key)
+		entry, ok := c.env[key]
 		if ok && (entry.dtype == dtype) {
 			return entry.parsed
 		}