diff --git a/src/zenity.ui b/src/zenity.ui
index ee89093..7c0ab1f 100644
--- a/src/zenity.ui
+++ b/src/zenity.ui
@@ -1021,6 +1021,7 @@
                 <property name="visible">True</property>
                 <property name="can_focus">True</property>
                 <property name="shadow_type">in</property>
+                <property name="expand">True</property>
                 <child>
                   <object class="GtkTreeView" id="zenity_tree_view">
                     <property name="visible">True</property>