diff --git a/src/corelib/tools/qcontainerfwd.h b/src/corelib/tools/qcontainerfwd.h
index 60cf04e3c6e..fa0fc877285 100644
--- a/src/corelib/tools/qcontainerfwd.h
+++ b/src/corelib/tools/qcontainerfwd.h
@@ -30,7 +30,8 @@ template <typename T> class QQueue;
 template <typename T> class QSet;
 template <typename T, std::size_t E = std::size_t(-1) /* = std::dynamic_extent*/> class QSpan;
 template <typename T> class QStack;
-template <typename T, qsizetype Prealloc = 256> class QVarLengthArray;
+constexpr qsizetype QVarLengthArrayDefaultPrealloc = 256;
+template <typename T, qsizetype Prealloc = QVarLengthArrayDefaultPrealloc> class QVarLengthArray;
 template <typename T> class QList;
 class QString;
 #ifndef Q_QDOC
diff --git a/src/corelib/tools/qflatmap_p.h b/src/corelib/tools/qflatmap_p.h
index 7fce7c43af0..d2c0d45b79d 100644
--- a/src/corelib/tools/qflatmap_p.h
+++ b/src/corelib/tools/qflatmap_p.h
@@ -1099,7 +1099,9 @@ private:
     containers c;
 };
 
-template<class Key, class T, qsizetype N = 256, class Compare = std::less<Key>>
+template <class Key, class T,
+          qsizetype N = QVarLengthArrayDefaultPrealloc,
+          class Compare = std::less<Key>>
 using QVarLengthFlatMap = QFlatMap<Key, T, Compare, QVarLengthArray<Key, N>, QVarLengthArray<T, N>>;
 
 QT_END_NAMESPACE