diff --git a/src/main/java/org/orekit/rugged/atmosphericrefraction/MultiLayerModel.java b/src/main/java/org/orekit/rugged/atmosphericrefraction/MultiLayerModel.java
index 02cbf993ee8b189fa470b5803a5b1c6bca4d0ca2..452a6197ebde4e0019c9ea5555ba2530a60f3fb8 100644
--- a/src/main/java/org/orekit/rugged/atmosphericrefraction/MultiLayerModel.java
+++ b/src/main/java/org/orekit/rugged/atmosphericrefraction/MultiLayerModel.java
@@ -73,8 +73,8 @@ public class MultiLayerModel implements AtmosphericRefraction {
             throws OrekitException {
         this.ellipsoid = ellipsoid;
         this.refractionLayers = refractionLayers;
-        atmosphereLowestAltitude = refractionLayers.get(refractionLayers.size() - 1).getLowestAltitude();
         Collections.sort(this.refractionLayers, Collections.<ConstantRefractionLayer>reverseOrder());
+        atmosphereLowestAltitude = refractionLayers.get(refractionLayers.size() - 1).getLowestAltitude();
     }
 
     @Override