diff --git a/gtsam.h b/gtsam.h
index 09b5b59e6..c9364d9b0 100644
--- a/gtsam.h
+++ b/gtsam.h
@@ -1375,6 +1375,7 @@ virtual class Fair: gtsam::noiseModel::mEstimator::Base {
   void serializable() const;
 
   double weight(double error) const;
+  double residual(double error) const;
 };
 
 virtual class Huber: gtsam::noiseModel::mEstimator::Base {