diff --git a/gtsam/linear/NoiseModel.h b/gtsam/linear/NoiseModel.h
index cccca225b..2badad838 100644
--- a/gtsam/linear/NoiseModel.h
+++ b/gtsam/linear/NoiseModel.h
@@ -224,7 +224,9 @@ namespace gtsam {
       }
 
 #ifdef GTSAM_ALLOW_DEPRECATED_SINCE_V4
-      virtual double Mahalanobis(const Vector& v) const;
+      virtual double Mahalanobis(const Vector& v) const {
+        return squaredMahalanobisDistance(v);
+      }
 #endif
 
       inline virtual double error(const Vector& v) const {