diff --git a/internal/generator/accessor/doc.go b/internal/generator/accessor/doc.go
new file mode 100644
index 0000000..a88e328
--- /dev/null
+++ b/internal/generator/accessor/doc.go
@@ -0,0 +1,6 @@
+// Package accessor generates an accessor method for each type in "one-of
+// groups". While "protoc-gen-go" plugin already generates accessor methods for
+// for each type in "one-of groups", the generated methods lack the ability to
+// differentiate between the absence of a value and the presence of a zero
+// value.
+package accessor
diff --git a/internal/generator/accessor/generate.go b/internal/generator/accessor/generate.go
new file mode 100644
index 0000000..81d8d47
--- /dev/null
+++ b/internal/generator/accessor/generate.go
@@ -0,0 +1,20 @@
+package accessor
+
+import (
+	"github.com/dave/jennifer/jen"
+	"github.com/dogmatiq/primo/internal/generator/internal/scope"
+)
+
+// Generate generates accessor methods for each type in one-of group. In
+// contrast to already available accessor methods generated by "protoc-gen-go"
+// plugin, these accessor methods return a boolean value indicating whether the
+// value is present or not.
+func Generate(code *jen.File, f *scope.File) error {
+	for _, m := range f.Messages() {
+		for _, g := range m.OneOfGroups() {
+			generateForOneOf(code, g)
+		}
+	}
+
+	return nil
+}
diff --git a/internal/generator/accessor/oneof.go b/internal/generator/accessor/oneof.go
new file mode 100644
index 0000000..1e6a6a4
--- /dev/null
+++ b/internal/generator/accessor/oneof.go
@@ -0,0 +1,74 @@
+package accessor
+
+import (
+	"github.com/dave/jennifer/jen"
+	"github.com/dogmatiq/primo/internal/generator/internal/scope"
+)
+
+func generateForOneOf(code *jen.File, g *scope.OneOfGroup) {
+	for _, o := range g.Options {
+		oneOfAccessorTryFunc(code, o)
+	}
+}
+
+func oneOfAccessorTryFunc(code *jen.File, o *scope.OneOfOption) {
+	methodName := "Try" + o.DiscriminatorFieldName
+
+	code.
+		Commentf(
+			"%s returns the value of [%s] in one-of field x.%s.",
+			methodName,
+			o.DiscriminatorFieldName,
+			o.Group.GoFieldName,
+		)
+	code.Comment("")
+	code.Comment("ok returns false if the value of this type is not set.")
+
+	code.
+		Func().
+		Params(
+			jen.
+				Id("x").
+				Op("*").
+				Id(o.Group.Message.GoTypeName),
+		).
+		Id(methodName).
+		Params().
+		Params(
+			jen.
+				Id("v").
+				Add(o.Field.GoType()),
+			jen.
+				Id("ok").
+				Add(jen.Bool()),
+		).
+		Block(
+			jen.
+				If(
+					jen.List(
+						jen.Id("x"),
+						jen.Id("ok"),
+					).
+						Op(":=").
+						Id("x").
+						Dot("Get"+o.Group.GoFieldName).
+						Call().
+						Assert(
+							jen.Op("*").
+								Id(o.DiscriminatorTypeName),
+						).
+						Op(";").
+						Id("ok"),
+				).Block(
+				jen.Return(
+					jen.Id("x").
+						Dot(o.DiscriminatorFieldName),
+					jen.True(),
+				),
+			),
+			jen.Return(
+				jen.Id("v"),
+				jen.False(),
+			),
+		)
+}
diff --git a/internal/generator/generate.go b/internal/generator/generate.go
index 033a07b..0729de0 100644
--- a/internal/generator/generate.go
+++ b/internal/generator/generate.go
@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"github.com/dave/jennifer/jen"
+	"github.com/dogmatiq/primo/internal/generator/accessor"
 	"github.com/dogmatiq/primo/internal/generator/builder"
 	"github.com/dogmatiq/primo/internal/generator/exhaustiveswitch"
 	"github.com/dogmatiq/primo/internal/generator/internal/option"
@@ -38,6 +39,7 @@ func Generate(
 		builder.Generate,
 		exhaustiveswitch.Generate,
 		mutator.Generate,
+		accessor.Generate,
 	); err != nil {
 		res.Error = proto.String(err.Error())
 	}
diff --git a/internal/test/accessor/helper_test.go b/internal/test/accessor/helper_test.go
new file mode 100644
index 0000000..f1213ab
--- /dev/null
+++ b/internal/test/accessor/helper_test.go
@@ -0,0 +1,61 @@
+package accessor_test
+
+import (
+	reflect "reflect"
+	"testing"
+
+	"google.golang.org/protobuf/proto"
+)
+
+// testAccessor calls a mutator method to set the value and verifies that the
+// corresponding accessor returns the expected value and boolean ok value.
+func testAccessor[M proto.Message, T comparable](
+	t *testing.T,
+	mutator func(M, T),
+	accessor func(M) (T, bool),
+	want T,
+) {
+	t.Helper()
+
+	testAccessorFunc(
+		t,
+		mutator,
+		accessor,
+		want,
+		func(a, b T) bool { return a == b },
+	)
+}
+
+// testAccessorFunc calls a mutator method to set the value and verifies that the
+// corresponding accessor returns the expected value and boolean ok value.
+func testAccessorFunc[M proto.Message, T any](
+	t *testing.T,
+	mutate func(M, T),
+	access func(M) (T, bool),
+	want T,
+	eq func(T, T) bool,
+) {
+	t.Helper()
+
+	var m M
+	m = reflect.New(
+		reflect.TypeOf(m).Elem(),
+	).Interface().(M)
+
+	mutate(m, want)
+
+	got, gotOK := access(m)
+	if !gotOK {
+		t.Fatalf(
+			"accessor did not return expected ok as true",
+		)
+	}
+
+	if !eq(got, want) {
+		t.Fatalf(
+			"accessor did not return the expected value: got: %v, want: %v",
+			got,
+			want,
+		)
+	}
+}
diff --git a/internal/test/accessor/oneof.pb.go b/internal/test/accessor/oneof.pb.go
new file mode 100644
index 0000000..35a7dcf
--- /dev/null
+++ b/internal/test/accessor/oneof.pb.go
@@ -0,0 +1,205 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.33.0
+// 	protoc        v5.26.1
+// source: github.com/dogmatiq/primo/internal/test/accessor/oneof.proto
+
+package accessor
+
+import (
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+type OneOf struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// Types that are assignable to Group:
+	//
+	//	*OneOf_FieldA
+	//	*OneOf_FieldB
+	//	*OneOf_FieldC
+	Group isOneOf_Group `protobuf_oneof:"group"`
+}
+
+func (x *OneOf) Reset() {
+	*x = OneOf{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *OneOf) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*OneOf) ProtoMessage() {}
+
+func (x *OneOf) ProtoReflect() protoreflect.Message {
+	mi := &file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use OneOf.ProtoReflect.Descriptor instead.
+func (*OneOf) Descriptor() ([]byte, []int) {
+	return file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDescGZIP(), []int{0}
+}
+
+func (m *OneOf) GetGroup() isOneOf_Group {
+	if m != nil {
+		return m.Group
+	}
+	return nil
+}
+
+func (x *OneOf) GetFieldA() int32 {
+	if x, ok := x.GetGroup().(*OneOf_FieldA); ok {
+		return x.FieldA
+	}
+	return 0
+}
+
+func (x *OneOf) GetFieldB() int32 {
+	if x, ok := x.GetGroup().(*OneOf_FieldB); ok {
+		return x.FieldB
+	}
+	return 0
+}
+
+func (x *OneOf) GetFieldC() string {
+	if x, ok := x.GetGroup().(*OneOf_FieldC); ok {
+		return x.FieldC
+	}
+	return ""
+}
+
+type isOneOf_Group interface {
+	isOneOf_Group()
+}
+
+type OneOf_FieldA struct {
+	FieldA int32 `protobuf:"varint,1,opt,name=field_a,json=fieldA,proto3,oneof"` // note: two fields of the same type
+}
+
+type OneOf_FieldB struct {
+	FieldB int32 `protobuf:"varint,2,opt,name=field_b,json=fieldB,proto3,oneof"`
+}
+
+type OneOf_FieldC struct {
+	FieldC string `protobuf:"bytes,3,opt,name=field_c,json=fieldC,proto3,oneof"`
+}
+
+func (*OneOf_FieldA) isOneOf_Group() {}
+
+func (*OneOf_FieldB) isOneOf_Group() {}
+
+func (*OneOf_FieldC) isOneOf_Group() {}
+
+var File_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto protoreflect.FileDescriptor
+
+var file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDesc = []byte{
+	0x0a, 0x3c, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x64, 0x6f, 0x67,
+	0x6d, 0x61, 0x74, 0x69, 0x71, 0x2f, 0x70, 0x72, 0x69, 0x6d, 0x6f, 0x2f, 0x69, 0x6e, 0x74, 0x65,
+	0x72, 0x6e, 0x61, 0x6c, 0x2f, 0x74, 0x65, 0x73, 0x74, 0x2f, 0x61, 0x63, 0x63, 0x65, 0x73, 0x73,
+	0x6f, 0x72, 0x2f, 0x6f, 0x6e, 0x65, 0x6f, 0x66, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x13,
+	0x70, 0x72, 0x69, 0x6d, 0x6f, 0x2e, 0x74, 0x65, 0x73, 0x74, 0x2e, 0x6d, 0x75, 0x74, 0x61, 0x74,
+	0x6f, 0x72, 0x73, 0x22, 0x61, 0x0a, 0x05, 0x4f, 0x6e, 0x65, 0x4f, 0x66, 0x12, 0x19, 0x0a, 0x07,
+	0x66, 0x69, 0x65, 0x6c, 0x64, 0x5f, 0x61, 0x18, 0x01, 0x20, 0x01, 0x28, 0x05, 0x48, 0x00, 0x52,
+	0x06, 0x66, 0x69, 0x65, 0x6c, 0x64, 0x41, 0x12, 0x19, 0x0a, 0x07, 0x66, 0x69, 0x65, 0x6c, 0x64,
+	0x5f, 0x62, 0x18, 0x02, 0x20, 0x01, 0x28, 0x05, 0x48, 0x00, 0x52, 0x06, 0x66, 0x69, 0x65, 0x6c,
+	0x64, 0x42, 0x12, 0x19, 0x0a, 0x07, 0x66, 0x69, 0x65, 0x6c, 0x64, 0x5f, 0x63, 0x18, 0x03, 0x20,
+	0x01, 0x28, 0x09, 0x48, 0x00, 0x52, 0x06, 0x66, 0x69, 0x65, 0x6c, 0x64, 0x43, 0x42, 0x07, 0x0a,
+	0x05, 0x67, 0x72, 0x6f, 0x75, 0x70, 0x42, 0x32, 0x5a, 0x30, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62,
+	0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x64, 0x6f, 0x67, 0x6d, 0x61, 0x74, 0x69, 0x71, 0x2f, 0x70, 0x72,
+	0x69, 0x6d, 0x6f, 0x2f, 0x69, 0x6e, 0x74, 0x65, 0x72, 0x6e, 0x61, 0x6c, 0x2f, 0x74, 0x65, 0x73,
+	0x74, 0x2f, 0x61, 0x63, 0x63, 0x65, 0x73, 0x73, 0x6f, 0x72, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74,
+	0x6f, 0x33,
+}
+
+var (
+	file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDescOnce sync.Once
+	file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDescData = file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDesc
+)
+
+func file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDescGZIP() []byte {
+	file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDescOnce.Do(func() {
+		file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDescData = protoimpl.X.CompressGZIP(file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDescData)
+	})
+	return file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDescData
+}
+
+var file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_msgTypes = make([]protoimpl.MessageInfo, 1)
+var file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_goTypes = []interface{}{
+	(*OneOf)(nil), // 0: primo.test.mutators.OneOf
+}
+var file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_depIdxs = []int32{
+	0, // [0:0] is the sub-list for method output_type
+	0, // [0:0] is the sub-list for method input_type
+	0, // [0:0] is the sub-list for extension type_name
+	0, // [0:0] is the sub-list for extension extendee
+	0, // [0:0] is the sub-list for field type_name
+}
+
+func init() { file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_init() }
+func file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_init() {
+	if File_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*OneOf); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_msgTypes[0].OneofWrappers = []interface{}{
+		(*OneOf_FieldA)(nil),
+		(*OneOf_FieldB)(nil),
+		(*OneOf_FieldC)(nil),
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   1,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_goTypes,
+		DependencyIndexes: file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_depIdxs,
+		MessageInfos:      file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_msgTypes,
+	}.Build()
+	File_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto = out.File
+	file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_rawDesc = nil
+	file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_goTypes = nil
+	file_github_com_dogmatiq_primo_internal_test_accessor_oneof_proto_depIdxs = nil
+}
diff --git a/internal/test/accessor/oneof.proto b/internal/test/accessor/oneof.proto
new file mode 100644
index 0000000..1d9fcca
--- /dev/null
+++ b/internal/test/accessor/oneof.proto
@@ -0,0 +1,12 @@
+syntax = "proto3";
+package primo.test.mutators;
+
+option go_package = "github.com/dogmatiq/primo/internal/test/accessor";
+
+message OneOf {
+  oneof group {
+    int32 field_a = 1; // note: two fields of the same type
+    int32 field_b = 2;
+    string field_c = 3;
+  }
+}
diff --git a/internal/test/accessor/oneof_test.go b/internal/test/accessor/oneof_test.go
new file mode 100644
index 0000000..acd6b92
--- /dev/null
+++ b/internal/test/accessor/oneof_test.go
@@ -0,0 +1,71 @@
+package accessor_test
+
+import (
+	"testing"
+
+	. "github.com/dogmatiq/primo/internal/test/accessor"
+)
+
+func TestOneOfAccessor(t *testing.T) {
+	t.Parallel()
+
+	t.Run("it returns the set value and ok as true to signify the presence of the value", func(t *testing.T) {
+		testAccessor(
+			t,
+			(*OneOf).SetFieldA,
+			(*OneOf).TryFieldA,
+			123,
+		)
+
+		testAccessor(
+			t,
+			(*OneOf).SetFieldA,
+			(*OneOf).TryFieldA,
+			0,
+		)
+
+		testAccessor(
+			t,
+			(*OneOf).SetFieldB,
+			(*OneOf).TryFieldB,
+			456,
+		)
+
+		testAccessor(
+			t,
+			(*OneOf).SetFieldB,
+			(*OneOf).TryFieldB,
+			0,
+		)
+
+		testAccessor(
+			t,
+			(*OneOf).SetFieldC,
+			(*OneOf).TryFieldC,
+			"<value>",
+		)
+
+		testAccessor(
+			t,
+			(*OneOf).SetFieldC,
+			(*OneOf).TryFieldC,
+			"",
+		)
+	})
+
+	t.Run("it ok as false to signify the absence of the value", func(t *testing.T) {
+		m := &OneOf{}
+
+		if _, ok := m.TryFieldA(); ok {
+			t.Fatalf("TryFieldA() returned ok as true, want false")
+		}
+
+		if _, ok := m.TryFieldB(); ok {
+			t.Fatalf("TryFieldB() returned ok as true, want false")
+		}
+
+		if _, ok := m.TryFieldC(); ok {
+			t.Fatalf("TryFieldC() returned ok as true, want false")
+		}
+	})
+}