diff --git a/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.cpp b/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.cpp
index f0c7212c8..1b7f86d5c 100644
--- a/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.cpp
+++ b/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.cpp
@@ -43,7 +43,7 @@ bool ConcurrentIncrementalFilter::equals(const ConcurrentFilter& rhs, double tol
 
 /* ************************************************************************* */
 ConcurrentIncrementalFilter::Result ConcurrentIncrementalFilter::update(const NonlinearFactorGraph& newFactors, const Values& newTheta,
-    const boost::optional<FastList<Key> >& keysToMove, const boost::optional< std::vector<size_t> >& removeFactorIndices) {
+    const boost::optional<FastList<Key> >& keysToMove, const boost::optional< FactorIndices >& removeFactorIndices) {
 
   gttic(update);
 
@@ -117,7 +117,7 @@ ConcurrentIncrementalFilter::Result ConcurrentIncrementalFilter::update(const No
 
     gttic(cache_smoother_factors);
     // Find the set of factors that will be removed
-    std::vector<size_t> removedFactorSlots = FindAdjacentFactors(isam2_, *keysToMove, currentSmootherSummarizationSlots_);
+    FactorIndices removedFactorSlots = FindAdjacentFactors(isam2_, *keysToMove, currentSmootherSummarizationSlots_);
     // Cache these factors for later transmission to the smoother
     NonlinearFactorGraph removedFactors;
     BOOST_FOREACH(size_t slot, removedFactorSlots) {
@@ -134,8 +134,8 @@ ConcurrentIncrementalFilter::Result ConcurrentIncrementalFilter::update(const No
     gttoc(cache_smoother_factors);
 
     gttic(marginalize);
-    std::vector<size_t> marginalFactorsIndices;
-    std::vector<size_t> deletedFactorsIndices;
+    FactorIndices marginalFactorsIndices;
+    FactorIndices deletedFactorsIndices;
     isam2_.marginalizeLeaves(*keysToMove, marginalFactorsIndices, deletedFactorsIndices);
     currentSmootherSummarizationSlots_.insert(currentSmootherSummarizationSlots_.end(), marginalFactorsIndices.begin(), marginalFactorsIndices.end());
     BOOST_FOREACH(size_t index, deletedFactorsIndices) {
@@ -285,10 +285,10 @@ void ConcurrentIncrementalFilter::RecursiveMarkAffectedKeys(const Key& key, cons
 }
 
 /* ************************************************************************* */
-std::vector<size_t> ConcurrentIncrementalFilter::FindAdjacentFactors(const ISAM2& isam2, const FastList<Key>& keys, const std::vector<size_t>& factorsToIgnore) {
+FactorIndices ConcurrentIncrementalFilter::FindAdjacentFactors(const ISAM2& isam2, const FastList<Key>& keys, const FactorIndices& factorsToIgnore) {
 
   // Identify any new factors to be sent to the smoother (i.e. any factor involving keysToMove)
-  std::vector<size_t> removedFactorSlots;
+  FactorIndices removedFactorSlots;
   const VariableIndex& variableIndex = isam2.getVariableIndex();
   BOOST_FOREACH(Key key, keys) {
     const FastVector<size_t>& slots = variableIndex[key];
diff --git a/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.h b/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.h
index 11012674e..c28b3bcd1 100644
--- a/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.h
+++ b/gtsam_unstable/nonlinear/ConcurrentIncrementalFilter.h
@@ -46,7 +46,7 @@ public:
      * factors passed as \c newFactors update().  These indices may be
      * used later to refer to the factors in order to remove them.
      */
-    std::vector<size_t> newFactorsIndices;
+    FactorIndices newFactorsIndices;
 
     double error; ///< The final factor graph error
 
@@ -124,7 +124,7 @@ public:
    */
   Result update(const NonlinearFactorGraph& newFactors = NonlinearFactorGraph(), const Values& newTheta = Values(),
       const boost::optional<FastList<Key> >& keysToMove = boost::none,
-      const boost::optional< std::vector<size_t> >& removeFactorIndices = boost::none);
+      const boost::optional< FactorIndices >& removeFactorIndices = boost::none);
 
   /**
    * Perform any required operations before the synchronization process starts.
@@ -170,7 +170,7 @@ protected:
 
   // ???
   NonlinearFactorGraph previousSmootherSummarization_; ///< The smoother summarization on the old separator sent by the smoother during the last synchronization
-  std::vector<size_t> currentSmootherSummarizationSlots_;  ///< The slots in factor graph that correspond to the current smoother summarization on the current separator
+  FactorIndices currentSmootherSummarizationSlots_;  ///< The slots in factor graph that correspond to the current smoother summarization on the current separator
   NonlinearFactorGraph smootherShortcut_; ///< A set of conditional factors from the old separator to the current separator (recursively calculated during each filter update)
 
   // Storage for information to be sent to the smoother
@@ -183,7 +183,7 @@ private:
   static void RecursiveMarkAffectedKeys(const Key& key, const ISAM2Clique::shared_ptr& clique, std::set<Key>& additionalKeys);
 
   /** Find the set of iSAM2 factors adjacent to 'keys' */
-  static std::vector<size_t> FindAdjacentFactors(const ISAM2& isam2, const FastList<Key>& keys, const std::vector<size_t>& factorsToIgnore);
+  static FactorIndices FindAdjacentFactors(const ISAM2& isam2, const FastList<Key>& keys, const FactorIndices& factorsToIgnore);
 
   /** Update the shortcut marginal between the current separator keys and the previous separator keys */
   // TODO: Make this a static function