diff --git a/tests/testsplitheaders.ui b/tests/testsplitheaders.ui
index ca68311b9c..66bfe4e6dd 100644
--- a/tests/testsplitheaders.ui
+++ b/tests/testsplitheaders.ui
@@ -24,6 +24,7 @@
         <child>
           <object class="GtkSeparator">
             <property name="visible">True</property>
+            <property name="orientation">vertical</property>
           </object>
         </child>
         <child>