diff --git a/src/corelib/compat/removed_api.cpp b/src/corelib/compat/removed_api.cpp
index 5ee844409a0..4a9cef2d41e 100644
--- a/src/corelib/compat/removed_api.cpp
+++ b/src/corelib/compat/removed_api.cpp
@@ -493,3 +493,19 @@ void QXmlStreamWriter::writeStartElement(const QString &namespaceUri, const QStr
 // order sections alphabetically to reduce chances of merge conflicts
 
 #endif // QT_CORE_REMOVED_SINCE(6, 5)
+
+#if QT_CORE_REMOVED_SINCE(6, 6)
+
+#include "qstring.h"
+
+qsizetype QString::toUcs4_helper(const ushort *uc, qsizetype length, uint *out)
+{
+    return toUcs4_helper(reinterpret_cast<const char16_t *>(uc), length,
+                         reinterpret_cast<char32_t *>(out));
+}
+
+// #include "qotherheader.h"
+// // implement removed functions from qotherheader.h
+// order sections alphabetically to reduce chances of merge conflicts
+
+#endif // QT_CORE_REMOVED_SINCE(6, 6)
diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index e2eb27a4d4b..d0836c3b929 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -2419,7 +2419,7 @@ void qtWarnAboutInvalidRegularExpression(const QString &pattern, const char *whe
         toStdU32String()
 */
 
-qsizetype QString::toUcs4_helper(const ushort *uc, qsizetype length, uint *out)
+qsizetype QString::toUcs4_helper(const char16_t *uc, qsizetype length, char32_t *out)
 {
     qsizetype count = 0;
 
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index b1ab89ec725..1da4fada9c9 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -859,7 +859,10 @@ private:
     static QByteArray toLatin1_helper_inplace(QString &);
     static QByteArray toUtf8_helper(const QString &);
     static QByteArray toLocal8Bit_helper(const QChar *data, qsizetype size);
-    static qsizetype toUcs4_helper(const ushort *uc, qsizetype length, uint *out); // ### Qt 7 char16_t
+#if QT_CORE_REMOVED_SINCE(6, 6)
+    static qsizetype toUcs4_helper(const ushort *uc, qsizetype length, uint *out);
+#endif
+    static qsizetype toUcs4_helper(const char16_t *uc, qsizetype length, char32_t *out);
     static qlonglong toIntegral_helper(QStringView string, bool *ok, int base);
     static qulonglong toIntegral_helper(QStringView string, bool *ok, uint base);
     void replace_helper(size_t *indices, qsizetype nIndices, qsizetype blen, const QChar *after, qsizetype alen);
@@ -1031,8 +1034,7 @@ qsizetype QStringView::toWCharArray(wchar_t *array) const
             memcpy(array, src, sizeof(QChar) * size());
         return size();
     } else {
-        return QString::toUcs4_helper(reinterpret_cast<const ushort *>(data()), size(),
-                                      reinterpret_cast<uint *>(array));
+        return QString::toUcs4_helper(utf16(), size(), reinterpret_cast<char32_t *>(array));
     }
 }
 
@@ -1228,8 +1230,8 @@ inline QString QString::fromStdU32String(const std::u32string &s)
 inline std::u32string QString::toStdU32String() const
 {
     std::u32string u32str(size(), char32_t(0));
-    qsizetype len = toUcs4_helper(reinterpret_cast<const ushort *>(constData()),
-                                  size(), reinterpret_cast<uint*>(&u32str[0]));
+    const qsizetype len = toUcs4_helper(reinterpret_cast<const char16_t *>(data()),
+                                        size(), u32str.data());
     u32str.resize(len);
     return u32str;
 }