diff --git a/Userland/Services/WindowServer/ConnectionFromClient.cpp b/Userland/Services/WindowServer/ConnectionFromClient.cpp
index dcb57422e7..4bac3d938a 100644
--- a/Userland/Services/WindowServer/ConnectionFromClient.cpp
+++ b/Userland/Services/WindowServer/ConnectionFromClient.cpp
@@ -625,11 +625,6 @@ void ConnectionFromClient::create_window(i32 window_id, Gfx::IntRect const& rect
             did_misbehave("CreateWindow with bad parent_window_id");
             return;
         }
-
-        if (auto* blocker = parent_window->blocking_modal_window(); blocker && mode == (i32)WindowMode::Blocking) {
-            did_misbehave("CreateWindow with illegal mode: reciprocally blocked");
-            return;
-        }
     }
 
     if (type < 0 || type >= (i32)WindowType::_Count) {
@@ -649,6 +644,11 @@ void ConnectionFromClient::create_window(i32 window_id, Gfx::IntRect const& rect
 
     auto window = Window::construct(*this, (WindowType)type, (WindowMode)mode, window_id, minimizable, closeable, frameless, resizable, fullscreen, parent_window);
 
+    if (auto* blocker = window->blocking_modal_window(); blocker && mode == to_underlying(WindowMode::Blocking)) {
+        did_misbehave("CreateWindow with illegal mode: Reciprocally blocked");
+        return;
+    }
+
     window->set_forced_shadow(forced_shadow);
 
     if (!launch_origin_rect.is_empty())
@@ -1361,6 +1361,12 @@ void ConnectionFromClient::set_window_parent_from_client(i32 client_id, i32 pare
     } else {
         did_misbehave("SetWindowParentFromClient: Window is not stealable");
     }
+
+    auto is_also_blocking = to_underlying(child_window->mode()) == to_underlying(WindowMode::Blocking);
+    if (auto* blocker = child_window->blocking_modal_window(); blocker && is_also_blocking) {
+        did_misbehave("SetWindowParentFromClient: Reciprocally blocked");
+        return;
+    }
 }
 
 Messages::WindowServer::GetWindowRectFromClientResponse ConnectionFromClient::get_window_rect_from_client(i32 client_id, i32 window_id)
diff --git a/Userland/Services/WindowServer/Window.cpp b/Userland/Services/WindowServer/Window.cpp
index 809247f2e5..6e0f533111 100644
--- a/Userland/Services/WindowServer/Window.cpp
+++ b/Userland/Services/WindowServer/Window.cpp
@@ -689,6 +689,8 @@ bool Window::is_active() const
 Window* Window::blocking_modal_window()
 {
     auto maybe_blocker = WindowManager::the().for_each_window_in_modal_chain(*this, [&](auto& window) {
+        if (parent_window() == window.parent_window() && is_blocking())
+            return IterationDecision::Continue;
         if (is_descendant_of(window))
             return IterationDecision::Continue;
         if (window.is_blocking() && this != &window)
diff --git a/Userland/Services/WindowServer/WindowMode.h b/Userland/Services/WindowServer/WindowMode.h
index e6c7930adc..c872d62218 100644
--- a/Userland/Services/WindowServer/WindowMode.h
+++ b/Userland/Services/WindowServer/WindowMode.h
@@ -13,7 +13,7 @@ namespace WindowServer {
 // - Modeless:      No modal effect (default mode for parentless windows)
 // - Passive:       Joins the modal chain but has no modal effect (default mode for child windows)
 // - RenderAbove:   Renders above its parent
-// - Blocking:      Preempts all interaction with its modal chain excepting descendants and popups (default mode for Dialogs)
+// - Blocking:      Preempts all interaction with its modal chain excepting descendants, sibling blockers, and popups (default mode for Dialogs)
 enum class WindowMode {
     Modeless = 0,
     Passive,