diff --git a/gtsam_unstable/gtsam_unstable.i b/gtsam_unstable/gtsam_unstable.i
index 35d2da40f..7d5241771 100644
--- a/gtsam_unstable/gtsam_unstable.i
+++ b/gtsam_unstable/gtsam_unstable.i
@@ -566,10 +566,13 @@ virtual class FixedLagSmoother {
   gtsam::FixedLagSmootherKeyTimestampMap timestamps() const;
   double smootherLag() const;
 
+  gtsam::FixedLagSmootherResult update(const gtsam::NonlinearFactorGraph &newFactors,
+                                       const gtsam::Values &newTheta,
+                                       const gtsam::FixedLagSmootherKeyTimestampMap &timestamps);
   gtsam::FixedLagSmootherResult update(const gtsam::NonlinearFactorGraph &newFactors,
                                        const gtsam::Values &newTheta,
                                        const gtsam::FixedLagSmootherKeyTimestampMap &timestamps,
-                                       const gtsam::FactorIndices &factorsToRemove=gtsam::FactorIndices());
+                                       const gtsam::FactorIndices &factorsToRemove);
   gtsam::Values calculateEstimate() const;
 };