diff --git a/gtsam/slam/GPSFactor.h b/gtsam/slam/GPSFactor.h
index 7d720cd15..9add83be0 100644
--- a/gtsam/slam/GPSFactor.h
+++ b/gtsam/slam/GPSFactor.h
@@ -90,11 +90,6 @@ namespace gtsam {
       return measured_;
     }
 
-    /** number of variables attached to this factor */
-    size_t size() const {
-      return 2;
-    }
-
   private:
 
     /** Serialization function */