diff --git a/gtsam/navigation/NavState.h b/gtsam/navigation/NavState.h
index e9afcd3ac..f66e9d7a9 100644
--- a/gtsam/navigation/NavState.h
+++ b/gtsam/navigation/NavState.h
@@ -64,7 +64,7 @@ public:
       R_(pose.rotation()), t_(pose.translation()), v_(v) {
   }
   /// Construct from SO(3) and R^6
-  NavState(const Matrix3& R, const Vector9 tv) :
+  NavState(const Matrix3& R, const Vector6& tv) :
       R_(R), t_(tv.head<3>()), v_(tv.tail<3>()) {
   }
   /// Named constructor with derivatives