diff --git a/redo/windows/stddialogs.c b/redo/windows/stddialogs.c
index 52eeb9c3..082f6a3c 100644
--- a/redo/windows/stddialogs.c
+++ b/redo/windows/stddialogs.c
@@ -63,9 +63,6 @@ char *uiSaveFile(void)
 }
 
 // TODO MinGW-w64 3.x doesn't support task dialogs
-#define TDCBF_OK_BUTTON 0x0001
-#define TD_ERROR_ICON MAKEINTRESOURCEW(-2)
-typedef int TASKDIALOG_COMMON_BUTTON_FLAGS;           // Note: _TASKDIALOG_COMMON_BUTTON_FLAGS is an int
 HRESULT (*WINAPI fv_TaskDialog)(_In_opt_ HWND hwndOwner, _In_opt_ HINSTANCE hInstance, _In_opt_ PCWSTR pszWindowTitle, _In_opt_ PCWSTR pszMainInstruction, _In_opt_ PCWSTR pszContent, TASKDIALOG_COMMON_BUTTON_FLAGS dwCommonButtons, _In_opt_ PCWSTR pszIcon, int *pnButton) = NULL;
 
 static void msgbox(const char *title, const char *description, TASKDIALOG_COMMON_BUTTON_FLAGS buttons, PCWSTR icon)
diff --git a/redo/windows/uipriv_windows.h b/redo/windows/uipriv_windows.h
index 640dad04..e6a7490f 100644
--- a/redo/windows/uipriv_windows.h
+++ b/redo/windows/uipriv_windows.h
@@ -5,6 +5,13 @@
 #include "../uipriv.h"
 #include "resources.h"
 
+#ifndef __MINGW64_VERSION_MAJOR
+#error At present, only MinGW-w64 (>= 4.0.0) is supported. Other toolchains will be supported in the future (but other variants of MinGW will not).
+#endif
+#if __MINGW64_VERSION_MAJOR < 4
+#error MinGW-w64 version 4.0.0 or newer is required.
+#endif
+
 // ui internal window messages
 enum {
 	// redirected WM_COMMAND and WM_NOTIFY