diff --git a/lib/voicemeeter/base.rb b/lib/voicemeeter/base.rb
index f048958..467d6ff 100644
--- a/lib/voicemeeter/base.rb
+++ b/lib/voicemeeter/base.rb
@@ -218,7 +218,7 @@ module Voicemeeter
         case key.to_s.split("-")
         in [/strip|bus|button/ => kls, /^[0-9]+$/ => index]
           target = send(kls)
-        in ["vban", String => dir, /^[0-9]+$/ => index]
+        in ["vban", /in|instream|out|oustream/ => dir, /^[0-9]+$/ => index]
           target = vban.send("#{dir.chomp("stream")}stream")
         else
           raise KeyError, "invalid config key '#{key}'"