diff --git a/envconf.go b/envconf.go
index 849a968..da14de4 100644
--- a/envconf.go
+++ b/envconf.go
@@ -259,7 +259,7 @@ func (c *Config) Status() (ok bool) {
 }
 
 func cleanKey(key string) string {
-	expr := regexp.MustCompile("__+")
+	expr := regexp.MustCompile("(?:^_+)|(?:_+(?=_))|(?:_$)")
 	fn := func(r rune) rune {
 		if (r >= '0' && r <= '9') || (r >= 'A' && r <= 'Z') || r == '_' {
 			return r
@@ -268,7 +268,7 @@ func cleanKey(key string) string {
 	}
 
 	key = strings.Map(fn, strings.ToUpper(key))
-	return expr.ReplaceAllString(key, "_")
+	return expr.ReplaceAllString(key, "")
 }
 
 func keySplit(key string) (left string, right string, ok bool) {