diff --git a/cmd/cue/cmd/testdata/script/def_proto.txt b/cmd/cue/cmd/testdata/script/def_proto.txt
index 7708745..407b568 100644
--- a/cmd/cue/cmd/testdata/script/def_proto.txt
+++ b/cmd/cue/cmd/testdata/script/def_proto.txt
@@ -20,7 +20,7 @@
 }
 
 // The attribute value.
-Attributes_AttributeValue :: {
+Attributes_AttributeValue :: {} | {
 	stringValue: string @protobuf(2,name=string_value)
 } | {
 	int64Value: int64 @protobuf(3,name=int64_value)
diff --git a/encoding/protobuf/parse.go b/encoding/protobuf/parse.go
index e77db1f..c59f3f1 100644
--- a/encoding/protobuf/parse.go
+++ b/encoding/protobuf/parse.go
@@ -484,7 +484,7 @@
 
 	s := &ast.StructLit{
 		Lbrace: p.toCUEPos(v.Position),
-		// TOOD: set proto file position.
+		// TODO: set proto file position.
 		Rbrace: token.Newline.Pos(),
 	}
 
@@ -677,11 +677,7 @@
 func (p *protoConverter) oneOf(x *proto.Oneof) {
 	f := &ast.Field{
 		Label: p.ref(x.Position),
-		// TODO: Once we have closed structs, a oneOf is represented as a
-		// disjunction of empty structs and closed structs with required fields.
-		// For now we just specify the required fields. This is not correct
-		// but more practical.
-		// Value: &ast.StructLit{}, // Remove to make at least one required.
+		Value: &ast.StructLit{},
 		Token: token.ISA,
 	}
 	f.AddComment(comment(x.Comment, true))
diff --git a/encoding/protobuf/testdata/attributes.proto.out.cue b/encoding/protobuf/testdata/attributes.proto.out.cue
index dacadf7..bd16fa0 100644
--- a/encoding/protobuf/testdata/attributes.proto.out.cue
+++ b/encoding/protobuf/testdata/attributes.proto.out.cue
@@ -58,7 +58,7 @@
 }
 
 // The attribute value.
-Attributes_AttributeValue :: {
+Attributes_AttributeValue :: {} | {
 	// Used for values of type STRING, DNS_NAME, EMAIL_ADDRESS, and URI
 	stringValue: string @protobuf(2,name=string_value)
 } | {
diff --git a/encoding/protobuf/testdata/istio.io/api/mixer/v1/attributes_proto_gen.cue b/encoding/protobuf/testdata/istio.io/api/mixer/v1/attributes_proto_gen.cue
index dacadf7..bd16fa0 100644
--- a/encoding/protobuf/testdata/istio.io/api/mixer/v1/attributes_proto_gen.cue
+++ b/encoding/protobuf/testdata/istio.io/api/mixer/v1/attributes_proto_gen.cue
@@ -58,7 +58,7 @@
 }
 
 // The attribute value.
-Attributes_AttributeValue :: {
+Attributes_AttributeValue :: {} | {
 	// Used for values of type STRING, DNS_NAME, EMAIL_ADDRESS, and URI
 	stringValue: string @protobuf(2,name=string_value)
 } | {
diff --git a/encoding/protobuf/testdata/istio.io/api/mixer/v1/config/client/api_spec_proto_gen.cue b/encoding/protobuf/testdata/istio.io/api/mixer/v1/config/client/api_spec_proto_gen.cue
index 3e6c50e..09bd763 100644
--- a/encoding/protobuf/testdata/istio.io/api/mixer/v1/config/client/api_spec_proto_gen.cue
+++ b/encoding/protobuf/testdata/istio.io/api/mixer/v1/config/client/api_spec_proto_gen.cue
@@ -116,7 +116,7 @@
 	// example: GET, HEAD, POST, PUT, DELETE.
 	httpMethod?: string @protobuf(2,name=http_method)
 }
-HTTPAPISpecPattern :: {
+HTTPAPISpecPattern :: {} | {
 	// URI template to match against as defined by
 	// [rfc6570](https://tools.ietf.org/html/rfc6570). For example, the
 	// following are valid URI templates:
@@ -146,7 +146,7 @@
 // for a general overview of API keys as defined by OpenAPI.
 APIKey :: {
 }
-APIKey :: {
+APIKey :: {} | {
 	// API Key is sent as a query parameter. `query` represents the
 	// query string parameter name.
 	//
diff --git a/encoding/protobuf/testdata/istio.io/api/mixer/v1/config/client/quota_proto_gen.cue b/encoding/protobuf/testdata/istio.io/api/mixer/v1/config/client/quota_proto_gen.cue
index 6f02c1f..c02e3b3 100644
--- a/encoding/protobuf/testdata/istio.io/api/mixer/v1/config/client/quota_proto_gen.cue
+++ b/encoding/protobuf/testdata/istio.io/api/mixer/v1/config/client/quota_proto_gen.cue
@@ -74,7 +74,7 @@
 // case-sensitive.
 StringMatch :: {
 }
-StringMatch :: {
+StringMatch :: {} | {
 	// exact string match
 	exact: string @protobuf(1)
 } | {