diff --git a/gtsam.h b/gtsam.h
index 0ca70d389..71a14703e 100644
--- a/gtsam.h
+++ b/gtsam.h
@@ -232,7 +232,7 @@ class Rot3 {
   // Manifold
   static size_t Dim();
   size_t dim() const;
-  // gtsam::Rot3 retractCayley(Vector v) const; // not in Quaternion branch
+  // gtsam::Rot3 retractCayley(Vector v) const; // FIXME, does not exist in both Matrix and Quaternion options
   gtsam::Rot3 retract(Vector v) const;
   Vector localCoordinates(const gtsam::Rot3& p) const;