diff --git a/Userland/Libraries/LibGUI/Window.cpp b/Userland/Libraries/LibGUI/Window.cpp
index 02622d6c98..96fbdd0338 100644
--- a/Userland/Libraries/LibGUI/Window.cpp
+++ b/Userland/Libraries/LibGUI/Window.cpp
@@ -6,6 +6,7 @@
 
 #include <AK/Debug.h>
 #include <AK/HashMap.h>
+#include <AK/IDAllocator.h>
 #include <AK/JsonObject.h>
 #include <AK/NeverDestroyed.h>
 #include <AK/ScopeGuard.h>
@@ -30,6 +31,7 @@
 namespace GUI {
 
 static i32 s_next_backing_store_serial;
+static IDAllocator s_window_id_allocator;
 
 class WindowBackingStore {
 public:
@@ -118,7 +120,10 @@ void Window::show()
 
     auto* parent_window = find_parent_window();
 
-    m_window_id = WindowServerConnection::the().create_window(
+    m_window_id = s_window_id_allocator.allocate();
+
+    WindowServerConnection::the().async_create_window(
+        m_window_id,
         m_rect_when_windowless,
         !m_moved_by_client,
         m_has_alpha_channel,
diff --git a/Userland/Services/WindowServer/ClientConnection.cpp b/Userland/Services/WindowServer/ClientConnection.cpp
index e8ffe7d9ef..3ae815316b 100644
--- a/Userland/Services/WindowServer/ClientConnection.cpp
+++ b/Userland/Services/WindowServer/ClientConnection.cpp
@@ -460,7 +460,7 @@ Window* ClientConnection::window_from_id(i32 window_id)
     return it->value.ptr();
 }
 
-Messages::WindowServer::CreateWindowResponse ClientConnection::create_window(Gfx::IntRect const& rect,
+void ClientConnection::create_window(i32 window_id, Gfx::IntRect const& rect,
     bool auto_position, bool has_alpha_channel, bool modal, bool minimizable, bool resizable,
     bool fullscreen, bool frameless, bool accessory, float opacity, float alpha_hit_threshold,
     Gfx::IntSize const& base_size, Gfx::IntSize const& size_increment, Gfx::IntSize const& minimum_size,
@@ -471,16 +471,20 @@ Messages::WindowServer::CreateWindowResponse ClientConnection::create_window(Gfx
         parent_window = window_from_id(parent_window_id);
         if (!parent_window) {
             did_misbehave("CreateWindow with bad parent_window_id");
-            return nullptr;
+            return;
         }
     }
 
     if (type < 0 || type >= (i32)WindowType::_Count) {
         did_misbehave("CreateWindow with a bad type");
-        return nullptr;
+        return;
+    }
+
+    if (m_windows.contains(window_id)) {
+        did_misbehave("CreateWindow with already-used window ID");
+        return;
     }
 
-    int window_id = m_next_window_id++;
     auto window = Window::construct(*this, (WindowType)type, window_id, modal, minimizable, frameless, resizable, fullscreen, accessory, parent_window);
 
     window->set_has_alpha_channel(has_alpha_channel);
@@ -513,7 +517,6 @@ Messages::WindowServer::CreateWindowResponse ClientConnection::create_window(Gfx
     if (window->type() == WindowType::Applet)
         AppletManager::the().add_applet(*window);
     m_windows.set(window_id, move(window));
-    return window_id;
 }
 
 void ClientConnection::destroy_window(Window& window, Vector<i32>& destroyed_window_ids)
diff --git a/Userland/Services/WindowServer/ClientConnection.h b/Userland/Services/WindowServer/ClientConnection.h
index 045fc25b07..2564370a69 100644
--- a/Userland/Services/WindowServer/ClientConnection.h
+++ b/Userland/Services/WindowServer/ClientConnection.h
@@ -97,7 +97,7 @@ private:
     virtual void add_menu_item(i32, i32, i32, String const&, bool, bool, bool, bool, String const&, Gfx::ShareableBitmap const&, bool) override;
     virtual void add_menu_separator(i32) override;
     virtual void update_menu_item(i32, i32, i32, String const&, bool, bool, bool, bool, String const&) override;
-    virtual Messages::WindowServer::CreateWindowResponse create_window(Gfx::IntRect const&, bool, bool, bool,
+    virtual void create_window(i32, Gfx::IntRect const&, bool, bool, bool,
         bool, bool, bool, bool, bool, float, float, Gfx::IntSize const&, Gfx::IntSize const&, Gfx::IntSize const&,
         Optional<Gfx::IntSize> const&, i32, String const&, i32) override;
     virtual Messages::WindowServer::DestroyWindowResponse destroy_window(i32) override;
@@ -163,8 +163,6 @@ private:
 
     RefPtr<Core::Timer> m_ping_timer;
 
-    int m_next_window_id { 1982 };
-
     bool m_has_display_link { false };
     bool m_unresponsive { false };
 
diff --git a/Userland/Services/WindowServer/WindowServer.ipc b/Userland/Services/WindowServer/WindowServer.ipc
index 908c060797..09f8a27852 100644
--- a/Userland/Services/WindowServer/WindowServer.ipc
+++ b/Userland/Services/WindowServer/WindowServer.ipc
@@ -26,6 +26,7 @@ endpoint WindowServer
     update_menu_item(i32 menu_id, i32 identifier, i32 submenu_id, [UTF8] String text, bool enabled, bool checkable, bool checked, bool is_default, [UTF8] String shortcut) =|
 
     create_window(
+        i32 window_id,
         Gfx::IntRect rect,
         bool auto_position,
         bool has_alpha_channel,
@@ -43,7 +44,7 @@ endpoint WindowServer
         Optional<Gfx::IntSize> resize_aspect_ratio,
         i32 type,
         [UTF8] String title,
-        i32 parent_window_id) => (i32 window_id)
+        i32 parent_window_id) =|
 
     destroy_window(i32 window_id) => (Vector<i32> destroyed_window_ids)