--- a/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/WaterlevelGroundPanel.java	Mon Jan 13 11:52:22 2014 +0100
+++ b/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/WaterlevelGroundPanel.java	Mon Jan 20 12:44:16 2014 +0100
@@ -8,6 +8,8 @@
 
 package org.dive4elements.river.client.client.ui;
 
+import java.util.List;
+
 public class WaterlevelGroundPanel extends DistancePanel {
 
     private static final long serialVersionUID = 6598703468619862469L;
@@ -123,5 +125,16 @@
         // We don't need a helper panel here. But we have to override this
         // method to avoid the table creation in the parent class.
     }
+
+    @Override
+    protected void validateTo(List<String> errors) {
+        double to = distancePanel.getTo();
+
+        if (to < 0d) {
+            distancePanel.setTo(max);
+            errors.add(MSG.negative_values_not_allowed_for_to());
+        }
+        super.validateTo(errors);
+    }
 }
 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :