diff --git a/libraries/AP_NavEKF2/AP_NavEKF2_core.cpp b/libraries/AP_NavEKF2/AP_NavEKF2_core.cpp
index c910f73661..890d96b1e2 100644
--- a/libraries/AP_NavEKF2/AP_NavEKF2_core.cpp
+++ b/libraries/AP_NavEKF2/AP_NavEKF2_core.cpp
@@ -613,7 +613,7 @@ void NavEKF2_core::UpdateStrapdownEquationsNED()
  * The inspiration for using a complementary filter to correct for time delays in the EKF
  * is based on the work by A Khosravian.
  *
- * “Recursive Attitude Estimation in the Presence of Multi-rate and Multi-delay Vector Measurements”
+ * "Recursive Attitude Estimation in the Presence of Multi-rate and Multi-delay Vector Measurements"
  * A Khosravian, J Trumpf, R Mahony, T Hamel, Australian National University
 */
 void NavEKF2_core::calcOutputStates()