diff --git a/sw/airborne/fw_h_ctl.h b/sw/airborne/fw_h_ctl.h
index 421682752b..2506d160dc 100644
--- a/sw/airborne/fw_h_ctl.h
+++ b/sw/airborne/fw_h_ctl.h
@@ -36,7 +36,7 @@
 #include "paparazzi.h"
 
 /* outer loop parameters */
-extern float h_ctl_course_setpoint;
+extern float h_ctl_course_setpoint; /* rad, CW/north */
 extern float h_ctl_course_pre_bank;
 extern float h_ctl_course_pre_bank_correction;
 extern float h_ctl_course_pgain;