diff --git a/gtsam/linear/KalmanFilter.h b/gtsam/linear/KalmanFilter.h
index aeec47a39..df4cd1d65 100644
--- a/gtsam/linear/KalmanFilter.h
+++ b/gtsam/linear/KalmanFilter.h
@@ -17,6 +17,8 @@
  * @author Frank Dellaert
  */
 
+#pragma once
+
 #include <gtsam/linear/GaussianDensity.h>
 #include <gtsam/linear/NoiseModel.h>