diff --git a/kcmkwin/kwindesktop/main.ui b/kcmkwin/kwindesktop/main.ui
--- a/kcmkwin/kwindesktop/main.ui
+++ b/kcmkwin/kwindesktop/main.ui
@@ -92,6 +92,12 @@
             <property name="enabled">
              <bool>true</bool>
             </property>
+            <property name="minimum">
+             <number>1</number>
+            </property>
+            <property name="maximum">
+             <number>20</number>
+            </property>
            </widget>
           </item>
          </layout>