diff --git a/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.cpp b/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.cpp
index fbf7ac3e4..7a3cfe888 100644
--- a/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.cpp
+++ b/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.cpp
@@ -42,7 +42,8 @@ bool ConcurrentIncrementalFilter::equals(const ConcurrentFilter& rhs, double tol
 }
 
 /* ************************************************************************* */
-ConcurrentIncrementalFilter::Result ConcurrentIncrementalFilter::update(const NonlinearFactorGraph& newFactors, const Values& newTheta, const boost::optional<FastList<Key> >& keysToMove) {
+ConcurrentIncrementalFilter::Result ConcurrentIncrementalFilter::update(const NonlinearFactorGraph& newFactors, const Values& newTheta,
+    const boost::optional<FastList<Key> >& keysToMove, const boost::optional< std::vector<size_t> >& removeFactorIndices) {
 
   gttic(update);
 
@@ -54,8 +55,11 @@ ConcurrentIncrementalFilter::Result ConcurrentIncrementalFilter::update(const No
   // Create the return result meta-data
   Result result;
 
-  // We do not need to remove any factors at this time
+  // Remove any user-provided factors from iSAM2
   gtsam::FastVector<size_t> removedFactors;
+  if(removeFactorIndices){
+    removedFactors.insert(removedFactors.end(), removeFactorIndices->begin(), removeFactorIndices->end());
+  }
 
   // Generate ordering constraints that force the 'keys to move' to the end
   boost::optional<gtsam::FastMap<gtsam::Key,int> > orderingConstraints = boost::none;
@@ -147,7 +151,8 @@ ConcurrentIncrementalFilter::Result ConcurrentIncrementalFilter::update(const No
   result.iterations = 1;
   result.linearVariables = isam2_.getFixedVariables().size();
   result.nonlinearVariables = isam2_.getLinearizationPoint().size() - result.linearVariables;
-  result.error = isam2_.getFactorsUnsafe().error(isam2_.calculateEstimate());
+  result.newFactorsIndices = isam2Result.newFactorsIndices;
+//  result.error = isam2_.getFactorsUnsafe().error(isam2_.calculateEstimate());
 
   if(debug) std::cout << "ConcurrentIncrementalFilter::update  End" << std::endl;
 
diff --git a/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.h b/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.h
index bef94ef32..6e5216642 100644
--- a/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.h
+++ b/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.h
@@ -38,6 +38,7 @@ public:
     size_t iterations; ///< The number of optimizer iterations performed
     size_t nonlinearVariables; ///< The number of variables that can be relinearized
     size_t linearVariables; ///< The number of variables that must keep a constant linearization point
+    std::vector<size_t> newFactorsIndices; ///< The indices of the newly-added factors, in 1-to-1 correspondence with the factors passed in
     double error; ///< The final factor graph error
 
     /// Constructor
@@ -110,9 +111,11 @@ public:
    * You must include here all new variables occurring in newFactors that were not already
    * in the filter.
    * @param keysToMove An optional set of keys to move from the filter to the smoother
+   * @param removeFactorIndices An optional set of indices corresponding to the factors you want to remove from the graph
    */
   Result update(const NonlinearFactorGraph& newFactors = NonlinearFactorGraph(), const Values& newTheta = Values(),
-      const boost::optional<FastList<Key> >& keysToMove = boost::none);
+      const boost::optional<FastList<Key> >& keysToMove = boost::none,
+      const boost::optional< std::vector<size_t> >& removeFactorIndices = boost::none);
 
   /**
    * Perform any required operations before the synchronization process starts.