diff --git a/libraries/AP_HAL/RCOutput.h b/libraries/AP_HAL/RCOutput.h
index c3a10b7707..f18a9b2993 100644
--- a/libraries/AP_HAL/RCOutput.h
+++ b/libraries/AP_HAL/RCOutput.h
@@ -186,7 +186,9 @@ public:
     
     /*
       output modes. Allows for support of PWM, oneshot and dshot 
-     */
+    */
+    // this enum is used by BLH_OTYPE and ESC_PWM_TYPE on AP_Periph
+    // double check params are still correct when changing
     enum output_mode {
         MODE_PWM_NONE,
         MODE_PWM_NORMAL,