diff --git a/interface.go b/interface.go
index 5287a1d6c6fb6e090fe8e14a5f81bfaca18ad0de..fed7ac81b7b80e0d7d0fe2e2ccff4c5d58c7975a 100644
--- a/interface.go
+++ b/interface.go
@@ -56,6 +56,7 @@ const (
 	ComposeIn
 	ComposeOut
 	ComposeAtop
+	ComposeDstOver
 	ComposeDstIn
 	ComposeDstOut
 	ComposeDstAtop