diff --git a/internal/impl/decode.go b/internal/impl/decode.go
index 4441d4b..757bbde 100644
--- a/internal/impl/decode.go
+++ b/internal/impl/decode.go
@@ -136,7 +136,7 @@
 
 func (mi *MessageInfo) unmarshalExtension(b []byte, num wire.Number, wtyp wire.Type, exts map[int32]ExtensionField, opts unmarshalOptions) (n int, err error) {
 	x := exts[int32(num)]
-	xt := x.GetType()
+	xt := x.Type()
 	if xt == nil {
 		var err error
 		xt, err = opts.Resolver().FindExtensionByNumber(mi.Desc.FullName(), num)