diff --git a/doc.go b/doc.go
index 0b3918c0c..d6d6cf13d 100644
--- a/doc.go
+++ b/doc.go
@@ -92,4 +92,6 @@
 // to manage threads yourself. Functions like IsKeyPressed will no longer be concurrent-safe with this build tag.
 // They must be called from the main thread or the same goroutine as the given game's callback functions like Update
 // to RunGame.
+//
+// `microsoftgdk` is for Microsoft GDK (Xbox).
 package ebiten