diff --git a/internal/core/adt/composite.go b/internal/core/adt/composite.go
index 5e2f611..784e648 100644
--- a/internal/core/adt/composite.go
+++ b/internal/core/adt/composite.go
@@ -378,10 +378,11 @@
 type OptionalType int
 
 const (
-	HasField OptionalType = 1 << iota
-	HasPattern
-	HasAdditional
-	IsOpen
+	HasField      OptionalType = 1 << iota // X: T
+	HasDynamic                             // (X): T or "\(X)": T
+	HasPattern                             // [X]: T
+	HasAdditional                          // ...T
+	IsOpen                                 // Defined for all fields
 )
 
 func (v *Vertex) Kind() Kind {
diff --git a/internal/core/eval/optionals.go b/internal/core/eval/optionals.go
index 8d77a57..6b17a8d 100644
--- a/internal/core/eval/optionals.go
+++ b/internal/core/eval/optionals.go
@@ -44,8 +44,12 @@
 			break
 		}
 	}
-	if o.bulk != nil {
-		mask |= adt.HasPattern
+	for _, b := range o.bulk {
+		if b.expr == nil {
+			mask |= adt.HasDynamic
+		} else {
+			mask |= adt.HasPattern
+		}
 	}
 	if o.additional != nil {
 		mask |= adt.HasAdditional
diff --git a/internal/core/eval/optionals_test.go b/internal/core/eval/optionals_test.go
new file mode 100644
index 0000000..4d5c97c
--- /dev/null
+++ b/internal/core/eval/optionals_test.go
@@ -0,0 +1,76 @@
+// Copyright 2020 CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package eval_test
+
+import (
+	"testing"
+
+	"cuelang.org/go/cue/parser"
+	"cuelang.org/go/internal/core/adt"
+	"cuelang.org/go/internal/core/compile"
+	"cuelang.org/go/internal/core/eval"
+	"cuelang.org/go/internal/core/runtime"
+)
+
+func TestOptionalTypes(t *testing.T) {
+	testCases := []struct {
+		in  string
+		out adt.OptionalType
+	}{{
+		in: `
+		...
+		`,
+		out: adt.HasAdditional | adt.IsOpen,
+	}, {
+		in: `
+		[string]: int
+		`,
+		// adt.IsOpen means fully defined in this context, which this is not.
+		out: adt.HasPattern,
+	}, {
+		in: `
+		bar: 3          // Not counted, as it is not optional.
+		{[string]: int} // embedded into end result.
+		"\(bar)": int
+		`,
+		out: adt.HasPattern | adt.HasDynamic,
+	}, {
+		in: `
+		bar?: 3
+		`,
+		out: adt.HasField,
+	}}
+	for _, tc := range testCases {
+		t.Run("", func(t *testing.T) {
+			ctx := eval.NewContext(runtime.New(), nil)
+			f, err := parser.ParseFile("opt", tc.in)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			v, errs := compile.Files(nil, ctx, f)
+			if errs != nil {
+				t.Fatal(errs)
+			}
+
+			v.Finalize(ctx)
+
+			got := v.OptionalTypes()
+			if got != tc.out {
+				t.Errorf("got %x; want %x", got, tc.out)
+			}
+		})
+	}
+}