diff --git a/gtsam_unstable/slam/SmartStereoProjectionPoseFactor.h b/gtsam_unstable/slam/SmartStereoProjectionPoseFactor.h
index 93a83ab30..e5342e2b6 100644
--- a/gtsam_unstable/slam/SmartStereoProjectionPoseFactor.h
+++ b/gtsam_unstable/slam/SmartStereoProjectionPoseFactor.h
@@ -118,7 +118,7 @@ class SmartStereoProjectionPoseFactor : public SmartStereoProjectionFactor {
       const KeyFormatter& keyFormatter = DefaultKeyFormatter) const override;
 
   /// equals
-  virtual bool equals(const NonlinearFactor& p, double tol = 1e-9) const;
+  bool equals(const NonlinearFactor& p, double tol = 1e-9) const override;
 
   /**
    * error calculates the error of the factor.