diff --git a/services/user-service/internal/storage/mysql/user/invite_referrer.go b/services/user-service/internal/storage/mysql/user/invite_referrer.go
index 9f46803b..84dbef38 100644
--- a/services/user-service/internal/storage/mysql/user/invite_referrer.go
+++ b/services/user-service/internal/storage/mysql/user/invite_referrer.go
@@ -27,12 +27,16 @@ func (r *Repository) FindInviteReferrerByCode(ctx context.Context, appCode strin
 	row := r.db.QueryRowContext(ctx, `
 		SELECT `+userSelectColumns+`
 		FROM users
-		INNER JOIN user_invite_codes codes
-		  ON codes.app_code = users.app_code
-		 AND codes.owner_user_id = users.user_id
 		WHERE users.app_code = ?
-		  AND codes.code = ?
-		  AND codes.status = ?
+		  AND EXISTS (
+		    SELECT 1
+		    FROM user_invite_codes codes
+		    WHERE codes.app_code = users.app_code
+		      AND codes.owner_user_id = users.user_id
+		      AND codes.code = ?
+		      AND codes.status = ?
+		    LIMIT 1
+		  )
 		LIMIT 1
 	`, appCode, inviteCode, invitedomain.CodeStatusActive)
 	inviter, err := ScanUser(row)
diff --git a/services/user-service/internal/storage/mysql/user/invite_referrer_test.go b/services/user-service/internal/storage/mysql/user/invite_referrer_test.go
new file mode 100644
index 00000000..58322797
--- /dev/null
+++ b/services/user-service/internal/storage/mysql/user/invite_referrer_test.go
@@ -0,0 +1,61 @@
+package user_test
+
+import (
+	"context"
+	"testing"
+
+	userdomain "hyapp/services/user-service/internal/domain/user"
+	"hyapp/services/user-service/internal/testutil/mysqltest"
+)
+
+func TestFindInviteReferrerByCodeDoesNotAmbiguouslySelectUserProjection(t *testing.T) {
+	repo := mysqltest.NewRepository(t)
+	ctx := context.Background()
+
+	createInviteReferrerUser(t, repo, 12001, "166001", 1000)
+	inviter, err := repo.GetUser(ctx, 12001)
+	if err != nil {
+		t.Fatalf("get inviter failed: %v", err)
+	}
+	if inviter.InviteOverview.MyInviteCode == "" {
+		t.Fatalf("expected inviter primary invite code")
+	}
+
+	found, err := repo.FindInviteReferrerByCode(ctx, "lalu", inviter.InviteOverview.MyInviteCode)
+	if err != nil {
+		t.Fatalf("find invite referrer by code failed: %v", err)
+	}
+	if found.UserID != inviter.UserID {
+		t.Fatalf("invite referrer mismatch: got=%d want=%d", found.UserID, inviter.UserID)
+	}
+}
+
+func createInviteReferrerUser(t *testing.T, repo *mysqltest.Repository, userID int64, displayUserID string, nowMs int64) {
+	t.Helper()
+	err := repo.CreateUserWithIdentity(context.Background(), userdomain.User{
+		AppCode:                  "lalu",
+		UserID:                   userID,
+		DefaultDisplayUserID:     displayUserID,
+		CurrentDisplayUserID:     displayUserID,
+		CurrentDisplayUserIDKind: userdomain.DisplayUserIDKindDefault,
+		Username:                 "invite-referrer",
+		Gender:                   "male",
+		Country:                  "SG",
+		ProfileCompleted:         true,
+		ProfileCompletedAtMs:     nowMs,
+		Status:                   userdomain.StatusActive,
+		OnboardingStatus:         userdomain.OnboardingStatusCompleted,
+		CreatedAtMs:              nowMs,
+		UpdatedAtMs:              nowMs,
+	}, userdomain.Identity{
+		AppCode:              "lalu",
+		UserID:               userID,
+		DisplayUserID:        displayUserID,
+		DefaultDisplayUserID: displayUserID,
+		DisplayUserIDKind:    userdomain.DisplayUserIDKindDefault,
+		Status:               userdomain.DisplayUserIDStatusActive,
+	})
+	if err != nil {
+		t.Fatalf("create invite referrer user %d failed: %v", userID, err)
+	}
+}