diff --git a/src/Avalonia.Native/WindowImplBase.cs b/src/Avalonia.Native/WindowImplBase.cs
index 852317a793..eab3a2e3f9 100644
--- a/src/Avalonia.Native/WindowImplBase.cs
+++ b/src/Avalonia.Native/WindowImplBase.cs
@@ -51,11 +51,30 @@ namespace Avalonia.Native
 
             base.Init(handle);
 
+            int defaultWidth = 0, defaultHeight = 0;
+
+            // AppKit can transiently report [NSScreen screens] as empty -- or report screens
+            // whose bounds don't contain the last-known window position -- during a CGS
+            // demote/promote race after wake-from-sleep, headless boots, or Spaces
+            // transitions. FirstOrDefault keeps window construction resilient through that
+            // window: the window falls back to a default size and is repositioned on the next
+            // ScreenChanged event once the display server settles, mirroring X11Window.
+            // See https://github.com/AvaloniaUI/Avalonia/issues/18895
             var monitor = this.TryGetFeature<IScreenImpl>()!.AllScreens
                 .OrderBy(x => x.Scaling)
-                .First(m => m.Bounds.Contains(Position));
+                .FirstOrDefault(m => m.Bounds.Contains(Position));
 
-            Resize(new Size(monitor.WorkingArea.Width * 0.75d, monitor.WorkingArea.Height * 0.7d), WindowResizeReason.Layout);
+            if (monitor != null)
+            {
+                // Emulate Windows 7+ default window size behavior.
+                defaultWidth = (int)(monitor.WorkingArea.Width * 0.75d);
+                defaultHeight = (int)(monitor.WorkingArea.Height * 0.7d);
+            }
+
+            defaultWidth = Math.Max(defaultWidth, 300);
+            defaultHeight = Math.Max(defaultHeight, 200);
+
+            Resize(new Size(defaultWidth, defaultHeight), WindowResizeReason.Layout);
         }
 
         public void Activate()