diff --git a/server/internal/reward/store.go b/server/internal/reward/store.go
index 605c8ea..fd81f4e 100644
--- a/server/internal/reward/store.go
+++ b/server/internal/reward/store.go
@@ -152,5 +152,5 @@ func isDup(err error) bool {
 		return false
 	}
 	m := strings.ToLower(err.Error())
-	return strings.Contains(m, "unique") || strings.Contains(m, "duplicate") || strings.Contains(m, "constraint")
+	return strings.Contains(m, "unique") || strings.Contains(m, "duplicate")
 }
diff --git a/server/internal/reward/store_sqlite_test.go b/server/internal/reward/store_sqlite_test.go
index 1e34e2f..b927aed 100644
--- a/server/internal/reward/store_sqlite_test.go
+++ b/server/internal/reward/store_sqlite_test.go
@@ -74,3 +74,25 @@ func TestInsertClaimUniqueGuards(t *testing.T) {
 	}
 	tx3.Rollback()
 }
+
+func TestInsertReferralUniqueInviteeGuard(t *testing.T) {
+	db := openDB(t)
+	seedU(t, db, 1, "u1")
+	seedU(t, db, 2, "u2")
+	seedU(t, db, 3, "u3")
+	st := NewStore(db)
+	now := time.Now().UTC()
+
+	tx, _ := db.Begin()
+	if err := st.InsertReferralTx(context.Background(), tx, 1, 2, "dev", "reg_rewarded", &now, now); err != nil {
+		t.Fatal(err)
+	}
+	tx.Commit()
+
+	// 同一 invitee(2)被另一 inviter(3)再次绑定 → invitee_id UNIQUE 命中,返回 ErrClaimExists
+	tx2, _ := db.Begin()
+	if err := st.InsertReferralTx(context.Background(), tx2, 3, 2, "dev", "reg_rewarded", &now, now); err != ErrClaimExists {
+		t.Fatalf("dup invitee insert err = %v, want ErrClaimExists", err)
+	}
+	tx2.Rollback()
+}