diff --git a/internal/impl/decode.go b/internal/impl/decode.go
index f71d19d..4441d4b 100644
--- a/internal/impl/decode.go
+++ b/internal/impl/decode.go
@@ -40,6 +40,7 @@
 
 func (o unmarshalOptions) Options() proto.UnmarshalOptions {
 	return proto.UnmarshalOptions{
+		Merge:          true,
 		AllowPartial:   true,
 		DiscardUnknown: o.DiscardUnknown(),
 		Resolver:       o.Resolver(),