diff --git a/src/Ursa.Themes.Semi/Controls/UrsaWindow.axaml b/src/Ursa.Themes.Semi/Controls/UrsaWindow.axaml
index 886a061..ebe33e1 100644
--- a/src/Ursa.Themes.Semi/Controls/UrsaWindow.axaml
+++ b/src/Ursa.Themes.Semi/Controls/UrsaWindow.axaml
@@ -177,5 +177,8 @@
         <Style Selector="^:maximized /template/ PathIcon#PART_RestoreButtonIcon">
             <Setter Property="Data" Value="{DynamicResource WindowRestoreGlyph}" />
         </Style>
+        <Style Selector="^:fullscreen /template/ PathIcon#PART_FullScreenButtonIcon">
+            <Setter Property="Data" Value="{DynamicResource WindowCollapseGlyph}" />
+        </Style>
     </ControlTheme>
 </ResourceDictionary>
\ No newline at end of file