diff --git a/backend/internal/repository/user_profile_identity_repo.go b/backend/internal/repository/user_profile_identity_repo.go
index dbba364d..25990c52 100644
--- a/backend/internal/repository/user_profile_identity_repo.go
+++ b/backend/internal/repository/user_profile_identity_repo.go
@@ -9,10 +9,12 @@ import (
 	"time"
 	"unsafe"
 
+	entsql "entgo.io/ent/dialect/sql"
 	dbent "github.com/Wei-Shaw/sub2api/ent"
 	"github.com/Wei-Shaw/sub2api/ent/authidentity"
 	"github.com/Wei-Shaw/sub2api/ent/authidentitychannel"
 	"github.com/Wei-Shaw/sub2api/ent/identityadoptiondecision"
+	dbpredicate "github.com/Wei-Shaw/sub2api/ent/predicate"
 	infraerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
 	"github.com/Wei-Shaw/sub2api/internal/service"
 )
@@ -379,6 +381,24 @@ ON CONFLICT (user_id, provider_type, grant_reason) DO NOTHING`,
 
 func (r *userRepository) UpsertIdentityAdoptionDecision(ctx context.Context, input IdentityAdoptionDecisionInput) (*dbent.IdentityAdoptionDecision, error) {
 	client := clientFromContext(ctx, r.client)
+	if input.IdentityID != nil && *input.IdentityID > 0 {
+		if _, err := client.IdentityAdoptionDecision.Update().
+			Where(
+				identityadoptiondecision.IdentityIDEQ(*input.IdentityID),
+				dbpredicate.IdentityAdoptionDecision(func(s *entsql.Selector) {
+					col := s.C(identityadoptiondecision.FieldPendingAuthSessionID)
+					s.Where(entsql.Or(
+						entsql.IsNull(col),
+						entsql.NEQ(col, input.PendingAuthSessionID),
+					))
+				}),
+			).
+			ClearIdentityID().
+			Save(ctx); err != nil {
+			return nil, err
+		}
+	}
+
 	current, err := client.IdentityAdoptionDecision.Query().
 		Where(identityadoptiondecision.PendingAuthSessionIDEQ(input.PendingAuthSessionID)).
 		Only(ctx)
diff --git a/backend/internal/repository/user_profile_identity_repo_contract_test.go b/backend/internal/repository/user_profile_identity_repo_contract_test.go
index d24a7d83..c5d0d897 100644
--- a/backend/internal/repository/user_profile_identity_repo_contract_test.go
+++ b/backend/internal/repository/user_profile_identity_repo_contract_test.go
@@ -353,6 +353,45 @@ func (s *UserProfileIdentityRepoSuite) TestUpsertIdentityAdoptionDecision_Persis
 	s.Require().Equal(identity.Identity.ID, *loaded.IdentityID)
 }
 
+func (s *UserProfileIdentityRepoSuite) TestUpsertIdentityAdoptionDecision_ReassignsExistingIdentityReference() {
+	user := s.mustCreateUser("adoption-reassign")
+	identity, err := s.repo.CreateAuthIdentity(s.ctx, CreateAuthIdentityInput{
+		UserID: user.ID,
+		Canonical: AuthIdentityKey{
+			ProviderType:    "wechat",
+			ProviderKey:     "wechat-open",
+			ProviderSubject: "union-adoption-reassign",
+		},
+	})
+	s.Require().NoError(err)
+
+	firstSession := s.mustCreatePendingAuthSession(identity.IdentityRef())
+	firstDecision, err := s.repo.UpsertIdentityAdoptionDecision(s.ctx, IdentityAdoptionDecisionInput{
+		PendingAuthSessionID: firstSession.ID,
+		IdentityID:           &identity.Identity.ID,
+		AdoptDisplayName:     true,
+		AdoptAvatar:          false,
+	})
+	s.Require().NoError(err)
+	s.Require().NotNil(firstDecision.IdentityID)
+	s.Require().Equal(identity.Identity.ID, *firstDecision.IdentityID)
+
+	secondSession := s.mustCreatePendingAuthSession(identity.IdentityRef())
+	secondDecision, err := s.repo.UpsertIdentityAdoptionDecision(s.ctx, IdentityAdoptionDecisionInput{
+		PendingAuthSessionID: secondSession.ID,
+		IdentityID:           &identity.Identity.ID,
+		AdoptDisplayName:     false,
+		AdoptAvatar:          true,
+	})
+	s.Require().NoError(err)
+	s.Require().NotNil(secondDecision.IdentityID)
+	s.Require().Equal(identity.Identity.ID, *secondDecision.IdentityID)
+
+	reloadedFirst, err := s.repo.GetIdentityAdoptionDecisionByPendingAuthSessionID(s.ctx, firstSession.ID)
+	s.Require().NoError(err)
+	s.Require().Nil(reloadedFirst.IdentityID)
+}
+
 func (s *UserProfileIdentityRepoSuite) TestUserAvatarCRUDAndUserLookup() {
 	user := s.mustCreateUser("avatar")