diff --git a/reflect/prototype/protofile_desc.go b/reflect/prototype/protofile_desc.go
index 39331dbb..466e53e7 100644
--- a/reflect/prototype/protofile_desc.go
+++ b/reflect/prototype/protofile_desc.go
@@ -55,7 +55,7 @@ import (
 func NewFileFromDescriptorProto(fd *descriptorV1.FileDescriptorProto, r *protoregistry.Files) (protoreflect.FileDescriptor, error) {
 	var f File
 	switch fd.GetSyntax() {
-	case "proto2":
+	case "", "proto2":
 		f.Syntax = protoreflect.Proto2
 	case "proto3":
 		f.Syntax = protoreflect.Proto3