diff --git a/.changes/windows-fullscreen-undecorated.md b/.changes/windows-fullscreen-undecorated.md
new file mode 100644
index 000000000..2420f5858
--- /dev/null
+++ b/.changes/windows-fullscreen-undecorated.md
@@ -0,0 +1,5 @@
+---
+"tao": "patch"
+---
+
+On Windows, fix fullscreen for undecorated window have white borders.
\ No newline at end of file
diff --git a/src/platform_impl/windows/event_loop.rs b/src/platform_impl/windows/event_loop.rs
index caf53928c..cc8d22384 100644
--- a/src/platform_impl/windows/event_loop.rs
+++ b/src/platform_impl/windows/event_loop.rs
@@ -2101,6 +2101,7 @@ unsafe fn public_window_callback_inner<T: 'static>(
 
     win32wm::WM_NCCALCSIZE => {
       let window_flags = subclass_input.window_state.lock().window_flags();
+      let is_fullscreen = subclass_input.window_state.lock().fullscreen.is_some();
 
       if wparam == WPARAM(0) || window_flags.contains(WindowFlags::MARKER_DECORATIONS) {
         result = ProcResult::DefSubclassProc;
@@ -2141,7 +2142,7 @@ unsafe fn public_window_callback_inner<T: 'static>(
 
             params.rgrc[0] = rect;
           }
-        } else if window_flags.contains(WindowFlags::MARKER_UNDECORATED_SHADOW) {
+        } else if window_flags.contains(WindowFlags::MARKER_UNDECORATED_SHADOW) && !is_fullscreen {
           let params = &mut *(lparam.0 as *mut NCCALCSIZE_PARAMS);
           params.rgrc[0].top += 1;
           params.rgrc[0].bottom += 1;