--- a/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/DoubleRangePanel.java	Fri Feb 07 15:48:43 2014 +0100
+++ b/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/DoubleRangePanel.java	Tue Feb 11 12:37:16 2014 +0100
@@ -45,6 +45,9 @@
      * distance.*/
     public static final String FIELD_WIDTH = "step";
 
+    /** Whether or not negative 'to' values are allowed. */
+    protected boolean negativeToAllowed = true;
+
     /** The textboxes */
     protected FloatItem fromItem;
     protected FloatItem toItem;
@@ -153,6 +156,10 @@
         stepItem.setValue(f.format(steps));
     }
 
+    public void setNegativeToAllowed(boolean isAllowed) {
+        negativeToAllowed = isAllowed;
+    }
+
 
     public boolean validateForm() {
         try {
@@ -171,6 +178,9 @@
      * there are values that doesn't represent a valid float, an error is
      * displayed.
      *
+     * Also if negativeToAllowed is false, an error is registered if
+     * the 'to' field contains a negative value.
+     *
      * @param item The FormItem.
      */
     @SuppressWarnings("unchecked")
@@ -187,12 +197,14 @@
         @SuppressWarnings("rawtypes")
         Map errors     = getErrors();
 
+        Double d = 0d;
+
         try {
             if (v == null) {
                 throw new NumberFormatException("empty");
             }
 
-            f.parse(v);
+            d = f.parse(v);
 
             errors.remove(item.getFieldName());
         }
@@ -204,6 +216,17 @@
             valid = false;
         }
 
+        if (negativeToAllowed == false
+            && item.getFieldName().equals(FIELD_TO) && d < 0d) {
+            errors.put(item.getFieldName(), MESSAGES.toShouldNotBeNegative());
+
+            item.setValue("");
+
+            item.focusInItem();
+
+            valid = false;
+        }
+
         setErrors(errors, true);
 
         return valid;