diff --git a/libraries/AP_Airspeed/AP_Airspeed_SDP3X.cpp b/libraries/AP_Airspeed/AP_Airspeed_SDP3X.cpp
index a8e066c515..b68ef886fa 100644
--- a/libraries/AP_Airspeed/AP_Airspeed_SDP3X.cpp
+++ b/libraries/AP_Airspeed/AP_Airspeed_SDP3X.cpp
@@ -259,6 +259,10 @@ float AP_Airspeed_SDP3X::_correct_pressure(float press)
 
     // airspeed ratio
     float ratio = get_airspeed_ratio();
+    if (!is_positive(ratio)) {
+        // cope with AP_Periph where ratio is 0
+        ratio = 2.0;
+    }
 
     // calculate equivalent pressure correction. This formula comes
     // from turning the dv correction above into an equivalent