diff --git a/interface.go b/interface.go
index 5287a1d..fed7ac8 100644
--- a/interface.go
+++ b/interface.go
@@ -56,6 +56,7 @@ const (
 	ComposeIn
 	ComposeOut
 	ComposeAtop
+	ComposeDstOver
 	ComposeDstIn
 	ComposeDstOut
 	ComposeDstAtop