diff --git a/src/corelib/compat/removed_api.cpp b/src/corelib/compat/removed_api.cpp
index c2cff280011..dec623d3ff8 100644
--- a/src/corelib/compat/removed_api.cpp
+++ b/src/corelib/compat/removed_api.cpp
@@ -161,6 +161,8 @@ QByteArray QUrl::toAce(const QString &domain)
 
 #if QT_CORE_REMOVED_SINCE(6, 4)
 
+#include "qbytearray.h" // uses QT_CORE_INLINE_SINCE
+
 #include "qcalendar.h"
 
 QCalendar::QCalendar(QStringView name)
diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index 0c5bf462281..f728877e4a5 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -3480,11 +3480,6 @@ QByteArray QByteArray::rightJustified(qsizetype width, char fill, bool truncate)
     return result;
 }
 
-bool QByteArray::isNull() const noexcept
-{
-    return d->isNull();
-}
-
 auto QtPrivate::toSignedInteger(QByteArrayView data, int base) -> ParsedNumber<qlonglong>
 {
 #if defined(QT_CHECK_RANGE)
diff --git a/src/corelib/text/qbytearray.h b/src/corelib/text/qbytearray.h
index a43a1a41280..888c3b96d56 100644
--- a/src/corelib/text/qbytearray.h
+++ b/src/corelib/text/qbytearray.h
@@ -439,6 +439,7 @@ public:
     inline qsizetype count() const noexcept { return size(); }
 #endif
     inline qsizetype length() const noexcept { return size(); }
+    QT_CORE_INLINE_SINCE(6, 4)
     bool isNull() const noexcept;
 
     inline DataPointer &data_ptr() { return d; }
@@ -567,6 +568,13 @@ inline QByteArray &QByteArray::setNum(ulong n, int base)
 inline QByteArray &QByteArray::setNum(float n, char format, int precision)
 { return setNum(double(n), format, precision); }
 
+#if QT_CORE_INLINE_IMPL_SINCE(6, 4)
+bool QByteArray::isNull() const noexcept
+{
+    return d->isNull();
+}
+#endif
+
 #if !defined(QT_NO_DATASTREAM) || defined(QT_BOOTSTRAPPED)
 Q_CORE_EXPORT QDataStream &operator<<(QDataStream &, const QByteArray &);
 Q_CORE_EXPORT QDataStream &operator>>(QDataStream &, QByteArray &);