diff --git a/calcs/leeway.js b/calcs/leeway.js
index 76bf520..3f0c278 100644
--- a/calcs/leeway.js
+++ b/calcs/leeway.js
@@ -4,7 +4,7 @@ module.exports = function (app, plugin) {
     group: 'heading',
     optionKey: 'leeway',
     title: 'Leeway',
-    derivedFrom: ['navigation.attitude.roll', 'navigation.speedThroughWater'],
+    derivedFrom: ['navigation.attitude', 'navigation.speedThroughWater'],
     properties: {
       kFactor: {
         type: 'number',
@@ -13,12 +13,11 @@ module.exports = function (app, plugin) {
         default: 12
       }
     },
-    calculator: function (roll, stw) {
+    calculator: function (attitude, stw) {
       var kFactor = plugin.properties.heading.kFactor
-      var rollDegrees = roll / Math.PI * 360
+      var rollDegrees = attitude.roll / Math.PI * 360
       var stwKnots = stw * 1.94384
-      var leewayAngle =
-        kFactor * rollDegrees / Math.pow(stwKnots, 2) / 360 * Math.PI
+      var leewayAngle = stwKnots <= 0 ? 0 : kFactor * rollDegrees / Math.pow(stwKnots, 2) / 360 * Math.PI
       // app.debug('roll: ' + rollDegrees + ' stw: ' + stwKnots + ' knots => leeway: ' + leewayAngle/Math.PI*360)
       return [{ path: 'performance.leeway', value: leewayAngle }]
     }