diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index 1ff2721265..b13708752d 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -34,6 +34,14 @@
 
 #include <algorithm>
 
+#ifdef Q_OS_WIN
+#  if !defined(QT_BOOTSTRAPPED) && (defined(QT_NO_CAST_FROM_ASCII) || defined(QT_NO_CAST_FROM_BYTEARRAY))
+// MSVC requires this, but let's apply it to MinGW compilers too, just in case
+#    error "This file cannot be compiled with QT_NO_CAST_{TO,FROM}_ASCII, " \
+           "otherwise some QByteArray functions will not get exported."
+#  endif
+#endif
+
 QT_BEGIN_NAMESPACE
 
 Q_CONSTINIT const char QByteArray::_empty = '\0';
diff --git a/src/corelib/text/qchar.cpp b/src/corelib/text/qchar.cpp
index 4175b6c849..0b44b83a88 100644
--- a/src/corelib/text/qchar.cpp
+++ b/src/corelib/text/qchar.cpp
@@ -1,14 +1,6 @@
 // Copyright (C) 2022 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
-// Don't define it while compiling this module, or USERS of Qt will
-// not be able to link.
-#ifdef QT_NO_CAST_FROM_ASCII
-#  undef QT_NO_CAST_FROM_ASCII
-#endif
-#ifdef QT_NO_CAST_TO_ASCII
-#  undef QT_NO_CAST_TO_ASCII
-#endif
 #include "qchar.h"
 
 #include "qdatastream.h"
diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index 6ebd7debed..af77f5d5d3 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -51,6 +51,11 @@
 
 #ifdef Q_OS_WIN
 #  include <qt_windows.h>
+#  if !defined(QT_BOOTSTRAPPED) && (defined(QT_NO_CAST_FROM_ASCII) || defined(QT_NO_CAST_TO_ASCII))
+// MSVC requires this, but let's apply it to MinGW compilers too, just in case
+#    error "This file cannot be compiled with QT_NO_CAST_{TO,FROM}_ASCII, " \
+           "otherwise some QString functions will not get exported."
+#  endif
 #endif
 
 #ifdef truncate