--- a/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/bundu/QSeriesLengthPanel.java	Thu Aug 16 12:04:46 2018 +0200
+++ b/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/bundu/QSeriesLengthPanel.java	Thu Aug 16 15:47:10 2018 +0200
@@ -131,7 +131,10 @@
         final List<String> errors = new ArrayList<String>();
         errors.addAll(ValidationHelper.checkForEmpty(this.inputItem, this.MSG));
         try {
-            Integer.valueOf(this.inputItem.getValueAsString());
+            final int value = Integer.valueOf(this.inputItem.getValueAsString());
+            if (value <= 0) {
+                errors.add(this.MSG.error_invalid_integer_positive_required());
+            }
         }
         catch (final NumberFormatException e) {
             errors.add(this.MSG.error_invalid_integer());