diff --git a/extras.go b/extras.go
index f937899..7f2ed2a 100644
--- a/extras.go
+++ b/extras.go
@@ -50,6 +50,7 @@ func (f *FlagSet) ParseEnv(environ []string) error {
 			envKey = f.envPrefix + "_" + envKey
 		}
 		envKey = strings.Replace(envKey, "-", "_", -1)
+		envKey = strings.Replace(envKey, ".", "_", -1)
 
 		value, isSet := env[envKey]
 		if !isSet {