diff --git a/libraries/AP_Airspeed/AP_Airspeed.h b/libraries/AP_Airspeed/AP_Airspeed.h
index 02fbdf588f..e63c939bd4 100644
--- a/libraries/AP_Airspeed/AP_Airspeed.h
+++ b/libraries/AP_Airspeed/AP_Airspeed.h
@@ -83,7 +83,10 @@ public:
 
     // return true if airspeed is enabled
     bool enabled(uint8_t i) const {
-        return param[i].type.get() != TYPE_NONE;
+        if (i < AIRSPEED_MAX_SENSORS) {
+            return param[i].type.get() != TYPE_NONE;
+        }
+        return false;
     }
     bool enabled(void) const { return enabled(primary); }
 
@@ -92,8 +95,7 @@ public:
         state[primary].airspeed = airspeed;
     }
 
-    // return the differential pressure in Pascal for the last
-    // airspeed reading. Used by the calibration code
+    // return the differential pressure in Pascal for the last airspeed reading
     float get_differential_pressure(uint8_t i) const {
         return state[i].last_pressure;
     }
@@ -215,6 +217,8 @@ private:
     uint8_t primary;
     
     void read(uint8_t i);
+    // return the differential pressure in Pascal for the last airspeed reading for the requested instance
+    // returns 0 if the sensor is not enabled
     float get_pressure(uint8_t i);
     void update_calibration(uint8_t i, float raw_pressure);
     void update_calibration(uint8_t i, const Vector3f &vground, int16_t max_airspeed_allowed_during_cal);