diff --git a/gtsam/nonlinear/nonlinear.i b/gtsam/nonlinear/nonlinear.i
index 7d2911374..e227de37c 100644
--- a/gtsam/nonlinear/nonlinear.i
+++ b/gtsam/nonlinear/nonlinear.i
@@ -404,6 +404,7 @@ virtual class NonlinearOptimizerParams {
   bool isCholmod() const;
   bool isIterative() const;
 
+  // This only applies to python since matlab does not have lambda machinery.
   gtsam::NonlinearOptimizerParams::IterationHook iterationHook;
 };