diff --git a/source/lib/sysdep/os/win/wutil.cpp b/source/lib/sysdep/os/win/wutil.cpp
index 167598b6cc..705119fcbd 100644
--- a/source/lib/sysdep/os/win/wutil.cpp
+++ b/source/lib/sysdep/os/win/wutil.cpp
@@ -20,10 +20,6 @@
  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
-/*
- * various Windows-specific utilities
- */
-
 #include "precompiled.h"
 #include "lib/sysdep/os/win/wutil.h"
 
@@ -40,6 +36,7 @@
 #include <shlobj.h>	// SHGetFolderPath
 
 #include <SDL_loadso.h>
+#include <SDL_syswm.h>
 
 
 WINIT_REGISTER_EARLY_INIT(wutil_Init);
@@ -409,31 +406,21 @@ HMODULE wutil_LibModuleHandle()
 
 static HWND hAppWindow;
 
-static BOOL CALLBACK FindAppWindowByPid(HWND hWnd, LPARAM UNUSED(lParam))
+void wutil_SetAppWindow(SDL_Window* window)
 {
-	DWORD pid;
-	DWORD tid = GetWindowThreadProcessId(hWnd, &pid);
-	UNUSED2(tid);
+	SDL_SysWMinfo wmInfo;
+	SDL_VERSION(&wmInfo.version);
+	if (SDL_GetWindowWMInfo(window, &wmInfo) && wmInfo.subsystem == SDL_SYSWM_WINDOWS)
+		hAppWindow = wmInfo.info.win.window;
+}
 
-	if(pid == GetCurrentProcessId())
-	{
-		char windowName[100];
-		GetWindowTextA(hWnd, windowName, 99);
-		if (strcmp(windowName, main_window_name) == 0)
-			hAppWindow = hWnd;
-	}
-
-	return TRUE;	// keep calling
+void wutil_SetAppWindow(void* hwnd)
+{
+	hAppWindow = reinterpret_cast<HWND>(hwnd);
 }
 
 HWND wutil_AppWindow()
 {
-	if(!hAppWindow)
-	{
-		WARN_IF_FALSE(EnumWindows(FindAppWindowByPid, 0));
-		// (hAppWindow may still be 0 if we haven't created a window yet)
-	}
-
 	return hAppWindow;
 }
 
diff --git a/source/lib/sysdep/os/win/wutil.h b/source/lib/sysdep/os/win/wutil.h
index 6716372e5d..c93e70517d 100644
--- a/source/lib/sysdep/os/win/wutil.h
+++ b/source/lib/sysdep/os/win/wutil.h
@@ -201,6 +201,8 @@ extern HMODULE wutil_LibModuleHandle();
  **/
 extern HWND wutil_AppWindow();
 
+extern void wutil_SetAppWindow(void* hwnd);
+
 extern void wutil_EnableHiDPIOnWindows();
 
 #endif	// #ifndef INCLUDED_WUTIL
diff --git a/source/ps/VideoMode.cpp b/source/ps/VideoMode.cpp
index d4035c386b..7642cde319 100644
--- a/source/ps/VideoMode.cpp
+++ b/source/ps/VideoMode.cpp
@@ -48,6 +48,10 @@ int DEFAULT_FULLSCREEN_H = 768;
 } // anonymous namespace
 
 #if OS_WIN
+// We can't include wutil directly because GL headers conflict with Windows
+// until we use a proper GL loader.
+extern void wutil_SetAppWindow(SDL_Window* window);
+
 // After a proper HiDPI integration we should switch to manifest until
 // SDL has an implemented HiDPI on Windows.
 extern void wutil_EnableHiDPIOnWindows();
@@ -164,6 +168,11 @@ bool CVideoMode::SetVideoMode(int w, int h, int bpp, bool fullscreen)
 	else
 		SDL_SetWindowGrab(m_Window, SDL_FALSE);
 
+#if OS_WIN
+	// We need to set the window for an error dialog.
+	wutil_SetAppWindow(m_Window);
+#endif
+
 	m_IsFullscreen = fullscreen;
 
 	g_xres = m_CurrentW;
diff --git a/source/tools/atlas/AtlasUI/ScenarioEditor/ScenarioEditor.cpp b/source/tools/atlas/AtlasUI/ScenarioEditor/ScenarioEditor.cpp
index 799ec73a6c..57d54ee268 100644
--- a/source/tools/atlas/AtlasUI/ScenarioEditor/ScenarioEditor.cpp
+++ b/source/tools/atlas/AtlasUI/ScenarioEditor/ScenarioEditor.cpp
@@ -589,6 +589,10 @@ ScenarioEditor::ScenarioEditor(wxWindow* parent)
 
 	// Send setup messages to game engine:
 
+	// We need to set the window HWND for the error dialog instead of iteraing
+	// through all open windows on Windows.
+	POST_MESSAGE(InitAppWindow, (GetHandle()));
+
 	POST_MESSAGE(InitSDL, ());
 
 	POST_MESSAGE(SetCanvas, (static_cast<wxGLCanvas*>(canvas),
diff --git a/source/tools/atlas/GameInterface/Handlers/GraphicsSetupHandlers.cpp b/source/tools/atlas/GameInterface/Handlers/GraphicsSetupHandlers.cpp
index 79aa03ae3f..d969deff5a 100644
--- a/source/tools/atlas/GameInterface/Handlers/GraphicsSetupHandlers.cpp
+++ b/source/tools/atlas/GameInterface/Handlers/GraphicsSetupHandlers.cpp
@@ -41,13 +41,19 @@
 #include "ps/GameSetup/GameSetup.h"
 #include "renderer/Renderer.h"
 
-static InputProcessor g_Input;
+#if OS_WIN
+// We don't include wutil header directly to prevent including Windows headers.
+extern void wutil_SetAppWindow(void* hwnd);
+#endif
+
+namespace AtlasMessage
+{
+
+InputProcessor g_Input;
 
 // This keeps track of the last in-game user input.
 // It is used to throttle FPS to save CPU & GPU.
-static double last_user_activity;
-
-namespace AtlasMessage {
+double last_user_activity;
 
 // see comment in GameLoop.cpp about ah_display_error before using INIT_HAVE_DISPLAY_ERROR
 const int g_InitFlags = INIT_HAVE_VMODE|INIT_NO_GUI;
@@ -73,6 +79,15 @@ MESSAGEHANDLER(Init)
 	g_VideoMode.InitNonSDL();
 }
 
+MESSAGEHANDLER(InitAppWindow)
+{
+#if OS_WIN
+	wutil_SetAppWindow(msg->handle);
+#else
+	UNUSED2(msg);
+#endif
+}
+
 MESSAGEHANDLER(InitSDL)
 {
 	UNUSED2(msg);
@@ -254,4 +269,4 @@ MESSAGEHANDLER(RenderStyle)
 	g_Renderer.SetOverlayRenderMode(msg->wireframe ? EDGED_FACES : SOLID);
 }
 
-}
+} // namespace AtlasMessage
diff --git a/source/tools/atlas/GameInterface/Messages.h b/source/tools/atlas/GameInterface/Messages.h
index f20806d416..b82f30bf3a 100644
--- a/source/tools/atlas/GameInterface/Messages.h
+++ b/source/tools/atlas/GameInterface/Messages.h
@@ -37,6 +37,10 @@
 // Initialise some engine code. Must be called before anything else.
 MESSAGE(Init, );
 
+MESSAGE(InitAppWindow,
+		((void*, handle)) // Atlas Window handle.
+		);
+
 // Initialise SDL-related code. Must be called before SetCanvas and InitGraphics.
 MESSAGE(InitSDL, );