diff --git a/.changes/adjusted-rect.md b/.changes/adjusted-rect.md
new file mode 100644
index 000000000..fa7757d90
--- /dev/null
+++ b/.changes/adjusted-rect.md
@@ -0,0 +1,5 @@
+---
+"tao": "patch"
+---
+
+On Windows, fix regression caused undecorated window with shadows to be slightly larger on creation.
\ No newline at end of file
diff --git a/src/platform_impl/windows/window.rs b/src/platform_impl/windows/window.rs
index c571716cc..7e2dabd29 100644
--- a/src/platform_impl/windows/window.rs
+++ b/src/platform_impl/windows/window.rs
@@ -1213,8 +1213,23 @@ unsafe fn init<T: 'static>(
         bottom: h,
       };
       unsafe {
-        AdjustWindowRectEx(&mut rect, style, pl_attribs.menu.is_some(), ex_style)?;
+        AdjustWindowRectEx(
+          &mut rect,
+          window_flags.to_adjusted_window_styles().0,
+          pl_attribs.menu.is_some(),
+          ex_style,
+        )?;
       }
+
+      // account for the 1px we add on each side in WM_NCCALCSIZE
+      // to add shadow for undecorated windows
+      if window_flags.contains(WindowFlags::MARKER_UNDECORATED_SHADOW)
+        && !window_flags.contains(WindowFlags::MARKER_DECORATIONS)
+      {
+        rect.right += 2;
+        rect.bottom += 2;
+      }
+
       (rect.right - rect.left, rect.bottom - rect.top)
     };
 
diff --git a/src/platform_impl/windows/window_state.rs b/src/platform_impl/windows/window_state.rs
index 00d558d1d..2e14348eb 100644
--- a/src/platform_impl/windows/window_state.rs
+++ b/src/platform_impl/windows/window_state.rs
@@ -295,6 +295,17 @@ impl WindowFlags {
     (style, style_ex)
   }
 
+  /// Returns the appropriate window styles for `AdjustWindowRectEx`
+  pub fn to_adjusted_window_styles(self) -> (WINDOW_STYLE, WINDOW_EX_STYLE) {
+    let (mut style, style_ex) = self.to_window_styles();
+
+    if !self.contains(WindowFlags::MARKER_DECORATIONS) {
+      style &= !(WS_CAPTION | WS_THICKFRAME)
+    }
+
+    (style, style_ex)
+  }
+
   /// Adjust the window client rectangle to the return value, if present.
   fn apply_diff(mut self, window: HWND, mut new: WindowFlags) {
     self = self.mask();