diff --git a/src/corelib/time/qcalendarmath_p.h b/src/corelib/time/qcalendarmath_p.h
index c785803ce3d..03153b0eed1 100644
--- a/src/corelib/time/qcalendarmath_p.h
+++ b/src/corelib/time/qcalendarmath_p.h
@@ -108,10 +108,10 @@ template <unsigned b, typename Int> constexpr Int qMod(Int a) { return qDivMod<b
 
 namespace QRomanCalendrical {
 // Julian Day number of Gregorian 1 BCE, February 29th:
-constexpr qint64 LeapDayGregorian1Bce = 1721119;
+inline constexpr qint64 LeapDayGregorian1Bce = 1721119;
 // Aside from (maybe) some turns of centuries, one year in four is leap:
-constexpr unsigned FourYears = 4 * 365 + 1;
-constexpr unsigned FiveMonths = 31 + 30 + 31 + 30 + 31; // Mar-Jul or Aug-Dec.
+inline constexpr unsigned FourYears = 4 * 365 + 1;
+inline constexpr unsigned FiveMonths = 31 + 30 + 31 + 30 + 31; // Mar-Jul or Aug-Dec.
 
 constexpr auto yearMonthToYearDays(int year, int month)
 {
diff --git a/src/corelib/time/qdatetime_p.h b/src/corelib/time/qdatetime_p.h
index 02b047dd737..a1aa7fd76a4 100644
--- a/src/corelib/time/qdatetime_p.h
+++ b/src/corelib/time/qdatetime_p.h
@@ -129,20 +129,31 @@ Q_DECLARE_OPERATORS_FOR_FLAGS(QDateTimePrivate::TransitionOptions)
 namespace QtPrivate {
 namespace DateTimeConstants {
 using namespace std::chrono;
+inline
 constexpr qint64 SECS_PER_MIN = minutes::period::num;
+inline
 constexpr qint64 SECS_PER_HOUR = hours::period::num;
+inline
 constexpr qint64 SECS_PER_DAY = SECS_PER_HOUR * 24; // std::chrono::days is C++20
 
+inline
 constexpr qint64 MINS_PER_HOUR = std::ratio_divide<hours::period, minutes::period>::num;
 
+inline
 constexpr qint64 MSECS_PER_SEC = milliseconds::period::den;
+inline
 constexpr qint64 MSECS_PER_MIN = SECS_PER_MIN * MSECS_PER_SEC;
+inline
 constexpr qint64 MSECS_PER_HOUR = SECS_PER_HOUR * MSECS_PER_SEC;
+inline
 constexpr qint64 MSECS_PER_DAY = SECS_PER_DAY * MSECS_PER_SEC;
 
+inline
 constexpr qint64 JULIAN_DAY_FOR_EPOCH = 2440588; // result of QDate(1970, 1, 1).toJulianDay()
 
+inline
 constexpr qint64 JulianDayMax = Q_INT64_C( 784354017364);
+inline
 constexpr qint64 JulianDayMin = Q_INT64_C(-784350574879);
 }
 }