diff --git a/src/main/java/gov/usgs/earthquake/nshmp/calc/Transforms.java b/src/main/java/gov/usgs/earthquake/nshmp/calc/Transforms.java
index b8c59a40f7f02d8d68eac768f08203f0dae34fd8..07a8fa3891c09787fd22f33600d0f42e4eba8e0c 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/calc/Transforms.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/calc/Transforms.java
@@ -509,6 +509,10 @@ final class Transforms {
    * for sources in a cluster. Note that this is only to be used with cluster
    * sources as the weight of each magnitude variant is stored in the
    * HazardInput.rate field, which is kinda KLUDGY, but works.
+   *
+   * TODO: Investigate sensitivity to collapsing magnitude variants on each
+   * fault in a cluster [F1(M1,M2,M3), F2(M1 M2,M3), ...] versus doing each
+   * magnitude branch separately [(F1M1,F2M1,...), (F1M2,F2M2,...)]
    */
   private static final class ClusterGroundMotionsToCurves implements
       Function<ClusterGroundMotions, ClusterCurves> {