diff --git a/integration_tests/handler/contest_test.go b/integration_tests/handler/contest_test.go
index fb3a134c..6554c3b7 100644
--- a/integration_tests/handler/contest_test.go
+++ b/integration_tests/handler/contest_test.go
@@ -291,7 +291,13 @@ func TestEditContest(t *testing.T) {
 		"204 without change": {
 			http.StatusNoContent,
 			mockdata.ContestID3(),
-			schema.EditContestRequest{},
+			schema.EditContestRequest{
+				Duration: &schema.Duration{
+					// DurationのValidationで落とされるのでSinceも埋める
+					Since: mockdata.CloneMockContests()[2].Since,
+					Until: &until, // Untilはnilにすると「未定」に変更される
+				},
+			},
 			nil,
 		},
 		"400 invalid contestID": {
diff --git a/integration_tests/handler/project_test.go b/integration_tests/handler/project_test.go
index b4f47645..26f5f092 100644
--- a/integration_tests/handler/project_test.go
+++ b/integration_tests/handler/project_test.go
@@ -253,7 +253,16 @@ func TestEditProject(t *testing.T) {
 		"204 without changes": {
 			http.StatusNoContent,
 			mockdata.ProjectID2(),
-			schema.EditProjectRequest{},
+			schema.EditProjectRequest{
+				Duration: &schema.YearWithSemesterDuration{
+					// DurationのValidationで落とされるのでSinceも埋める
+					Since: schema.YearWithSemester{
+						Year:     mockdata.CloneMockProjects()[1].SinceYear,
+						Semester: schema.Semester(mockdata.CloneMockProjects()[1].SinceSemester),
+					},
+					Until: duration.Until, // Untilはnilにすると「未定」に変更される
+				},
+			},
 			nil,
 		},
 		"400 invalid projectID": {
diff --git a/internal/infrastructure/repository/contest_impl.go b/internal/infrastructure/repository/contest_impl.go
index 6971ce4f..82c90c34 100644
--- a/internal/infrastructure/repository/contest_impl.go
+++ b/internal/infrastructure/repository/contest_impl.go
@@ -3,6 +3,7 @@ package repository
 import (
 	"context"
 	"errors"
+	"time"
 
 	"github.com/gofrs/uuid"
 	"github.com/traPtitech/traPortfolio/internal/domain"
@@ -107,6 +108,16 @@ func (r *ContestRepository) CreateContest(ctx context.Context, args *repository.
 }
 
 func (r *ContestRepository) UpdateContest(ctx context.Context, contestID uuid.UUID, args *repository.UpdateContestArgs) error {
+	origin := &model.Contest{}
+	if err := r.h.
+		WithContext(ctx).
+		Where(&model.Contest{ID: contestID}).
+		First(origin).
+		Error; err != nil {
+		return err
+	}
+	untilEmpty := origin.Until.Equal(time.Time{})
+
 	changes := map[string]interface{}{}
 	if v, ok := args.Name.V(); ok {
 		changes["name"] = v
@@ -120,7 +131,7 @@ func (r *ContestRepository) UpdateContest(ctx context.Context, contestID uuid.UU
 	if v, ok := args.Since.V(); ok {
 		changes["since"] = v
 	}
-	if v, ok := args.Until.V(); ok {
+	if v, ok := args.Until.V(); ok == untilEmpty || v != origin.Until {
 		changes["until"] = v
 	}
 
@@ -130,14 +141,6 @@ func (r *ContestRepository) UpdateContest(ctx context.Context, contestID uuid.UU
 
 	var c model.Contest
 	err := r.h.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
-		if err := tx.
-			WithContext(ctx).
-			Where(&model.Contest{ID: contestID}).
-			First(&model.Contest{}).
-			Error; err != nil {
-			return err
-		}
-
 		if err := tx.
 			WithContext(ctx).
 			Model(&model.Contest{ID: contestID}).
diff --git a/internal/infrastructure/repository/contest_test.go b/internal/infrastructure/repository/contest_test.go
index d1285e65..d1532de0 100644
--- a/internal/infrastructure/repository/contest_test.go
+++ b/internal/infrastructure/repository/contest_test.go
@@ -3,6 +3,7 @@ package repository
 import (
 	"context"
 	"testing"
+	"time"
 
 	"github.com/gofrs/uuid"
 	"github.com/samber/lo"
@@ -12,6 +13,7 @@ import (
 	"github.com/traPtitech/traPortfolio/internal/infrastructure/external/mock_external"
 	"go.uber.org/mock/gomock"
 
+	"github.com/traPtitech/traPortfolio/internal/pkgs/optional"
 	"github.com/traPtitech/traPortfolio/internal/pkgs/random"
 	"github.com/traPtitech/traPortfolio/internal/usecases/repository"
 )
@@ -122,6 +124,7 @@ func Test_UpdateContest(t *testing.T) {
 
 	t.Run("update no fields", func(t *testing.T) {
 		args := &repository.UpdateContestArgs{}
+		args.Until = optional.New(contest.TimeEnd, contest.TimeEnd == time.Time{})
 		err := repo.UpdateContest(context.Background(), contest.ID, args)
 		assert.NoError(t, err)
 
@@ -130,6 +133,23 @@ func Test_UpdateContest(t *testing.T) {
 
 		assert.Equal(t, contest, gotContest)
 	})
+
+	t.Run("update until to nil", func(t *testing.T) {
+		argWithUntil := random.CreateContestArgs()
+		argWithUntil.Until = random.UpdateContestArgs().Since
+		contest, err := repo.CreateContest(context.Background(), argWithUntil)
+		assert.NoError(t, err)
+
+		argWithoutUntil := random.UpdateContestArgs()
+		argWithoutUntil.Until = optional.Of[time.Time]{}
+		err = repo.UpdateContest(context.Background(), contest.ID, argWithoutUntil)
+		assert.NoError(t, err)
+	})
+
+	t.Run("update failed: not contest id", func(t *testing.T) {
+		err = repo.UpdateContest(context.Background(), random.UUID(), &repository.UpdateContestArgs{})
+		assert.Error(t, err)
+	})
 }
 
 func Test_DeleteContest(t *testing.T) {
diff --git a/internal/infrastructure/repository/project_impl.go b/internal/infrastructure/repository/project_impl.go
index abd1ae8f..81938a71 100644
--- a/internal/infrastructure/repository/project_impl.go
+++ b/internal/infrastructure/repository/project_impl.go
@@ -138,6 +138,15 @@ func (r *ProjectRepository) CreateProject(ctx context.Context, args *repository.
 }
 
 func (r *ProjectRepository) UpdateProject(ctx context.Context, projectID uuid.UUID, args *repository.UpdateProjectArgs) error {
+	origin := &model.Project{}
+	if err := r.h.
+		WithContext(ctx).
+		Where(&model.Project{ID: projectID}).
+		First(origin).
+		Error; err != nil {
+		return err
+	}
+
 	changes := map[string]interface{}{}
 	if v, ok := args.Name.V(); ok {
 		changes["name"] = v
@@ -154,10 +163,16 @@ func (r *ProjectRepository) UpdateProject(ctx context.Context, projectID uuid.UU
 			changes["since_semester"] = ss
 		}
 	}
-	if uy, ok := args.UntilYear.V(); ok {
-		if us, ok := args.UntilSemester.V(); ok {
-			changes["until_year"] = uy
-			changes["until_semester"] = us
+	untilYear, validYear := args.UntilYear.V()
+	untilSemester, validSemester := args.UntilSemester.V()
+	if validYear == validSemester {
+		originUntil := domain.YearWithSemester{Year: origin.UntilYear, Semester: origin.UntilSemester}
+		argUntil := domain.YearWithSemester{Year: int(args.UntilYear.ValueOrZero()), Semester: int(args.UntilSemester.ValueOrZero())}
+		originValid := originUntil.IsValid()
+		// Untilが未定かどうかの状態が異なるか、Untilが異なる場合に更新
+		if validYear != originValid || (validYear && argUntil != originUntil) {
+			changes["until_year"] = untilYear
+			changes["until_semester"] = untilSemester
 		}
 	}
 
diff --git a/internal/infrastructure/repository/project_test.go b/internal/infrastructure/repository/project_test.go
index 64e95179..144fbfe7 100644
--- a/internal/infrastructure/repository/project_test.go
+++ b/internal/infrastructure/repository/project_test.go
@@ -146,8 +146,12 @@ func TestProjectRepository_UpdateProject(t *testing.T) {
 					project1.Duration.Since.Semester = int(ss)
 				}
 			}
-			if uy, ok := arg1.UntilYear.V(); ok {
-				if us, ok := arg1.UntilSemester.V(); ok {
+			uy, validYear := arg1.UntilYear.V()
+			us, validSemester := arg1.UntilSemester.V()
+			if validYear == validSemester {
+				originUntil, originValid := project1.Duration.Until.V()
+				argUntil := domain.YearWithSemester{Year: int(uy), Semester: int(us)}
+				if validYear != originValid || (validYear && argUntil != originUntil) {
 					project1.Duration.Until = optional.From(domain.YearWithSemester{
 						Year:     int(uy),
 						Semester: int(us),