1 files changed, 20 insertions, 5 deletions
diff --git a/src/qml/jsruntime/qv4dateobject.cpp b/src/qml/jsruntime/qv4dateobject.cpp
index 520b715189..cc89947cec 100644
--- a/src/qml/jsruntime/qv4dateobject.cpp
+++ b/src/qml/jsruntime/qv4dateobject.cpp
@@ -294,13 +294,28 @@ static double MakeDay(double year, double month, double day)
     if (month < 0)
         month += 12.0;
 
-    double d = DayFromYear(year);
-    bool leap = InLeapYear(d*msPerDay);
+    /* Quoting the spec:
 
-    d += DayFromMonth(month, leap);
-    d += day - 1;
+       Find a value t such that YearFromTime(t) is ym and MonthFromTime(t) is mn
+       and DateFromTime(t) is 1; but if this is not possible (because some
+       argument is out of range), return NaN.
+    */
+    double first = DayFromYear(year);
+    /* Beware floating-point glitches: don't test the first millisecond of a
+     * year, month or day when we could test a moment firmly in the interior of
+     * the interval. A rounding glitch might give the first millisecond to the
+     * preceding interval.
+     */
+    bool leap = InLeapYear((first + 60) * msPerDay);
 
-    return d;
+    first += DayFromMonth(month, leap);
+    const double t = first * msPerDay + msPerDay / 2; // Noon on the first of the month
+    Q_ASSERT(Day(t) == first);
+    if (YearFromTime(t) != year || MonthFromTime(t) != month || DateFromTime(t) != 1) {
+        qWarning("Apparently out-of-range date %.0f-%02.0f-%02.0f", year, month, day);
+        return qt_qnan();
+    }
+    return first + day - 1;
 }
 
 static inline double MakeDate(double day, double time)