diff --git a/gtsam.h b/gtsam.h
index 33d26d939..ee069e0d3 100644
--- a/gtsam.h
+++ b/gtsam.h
@@ -2047,6 +2047,7 @@ virtual class ISAM2  : gtsam::ISAM2BayesTree {
 
   gtsam::Values getLinearizationPoint() const;
   gtsam::Values calculateEstimate() const;
+  Matrix marginalCovariance(size_t key) const;
   gtsam::Values calculateBestEstimate() const;
   gtsam::VectorValues getDelta() const;
   gtsam::NonlinearFactorGraph getFactorsUnsafe() const;