diff --git a/js/public/Date.h b/js/public/Date.h
index 6199f9eca5df..5adc71a7ffa4 100644
--- a/js/public/Date.h
+++ b/js/public/Date.h
@@ -6,10 +6,46 @@
 #ifndef js_Date_h
 #define js_Date_h
 
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/MathAlgorithms.h"
+
 #include "jstypes.h"
 
+#include "js/Conversions.h"
+#include "js/Value.h"
+
 namespace JS {
 
+class ClippedTime
+{
+    double t;
+
+    /* ES5 15.9.1.14. */
+    double timeClip(double time) {
+        /* Steps 1-2. */
+        const double MaxTimeMagnitude = 8.64e15;
+        if (!mozilla::IsFinite(time) || mozilla::Abs(time) > MaxTimeMagnitude)
+            return JS::GenericNaN();
+
+        /* Step 3. */
+        return JS::ToInteger(time) + (+0.0);
+    }
+
+  public:
+    ClippedTime() : t(JS::GenericNaN()) {}
+    explicit ClippedTime(double time) : t(timeClip(time)) {}
+
+    static ClippedTime NaN() { return ClippedTime(); }
+
+    double value() const { return t; }
+};
+
+inline ClippedTime
+TimeClip(double d)
+{
+    return ClippedTime(d);
+}
+
 // Year is a year, month is 0-11, day is 1-based.  The return value is
 // a number of milliseconds since the epoch.  Can return NaN.
 JS_PUBLIC_API(double)
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 81be0cf34de2..ec3e4065cabb 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -61,6 +61,7 @@
 #include "jit/JitCommon.h"
 #include "js/CharacterEncoding.h"
 #include "js/Conversions.h"
+#include "js/Date.h"
 #include "js/Proxy.h"
 #include "js/SliceBudget.h"
 #include "js/StructuredClone.h"
@@ -5237,7 +5238,7 @@ JS_NewDateObjectMsec(JSContext* cx, double msec)
 {
     AssertHeapIsIdle(cx);
     CHECK_REQUEST(cx);
-    return NewDateObjectMsec(cx, msec);
+    return NewDateObjectMsec(cx, JS::TimeClip(msec));
 }
 
 JS_PUBLIC_API(bool)
diff --git a/js/src/jsdate.cpp b/js/src/jsdate.cpp
index f4f28762f5be..ea3bbdd4ccc4 100644
--- a/js/src/jsdate.cpp
+++ b/js/src/jsdate.cpp
@@ -50,9 +50,12 @@ using namespace js;
 using mozilla::ArrayLength;
 using mozilla::IsFinite;
 using mozilla::IsNaN;
+using mozilla::NumbersAreIdentical;
 
 using JS::AutoCheckCannotGC;
+using JS::ClippedTime;
 using JS::GenericNaN;
+using JS::TimeClip;
 using JS::ToInteger;
 
 /*
@@ -350,7 +353,7 @@ MakeDate(double day, double time)
 JS_PUBLIC_API(double)
 JS::MakeDate(double year, unsigned month, unsigned day)
 {
-    return TimeClip(::MakeDate(MakeDay(year, month, day), 0));
+    return TimeClip(::MakeDate(MakeDay(year, month, day), 0)).value();
 }
 
 JS_PUBLIC_API(double)
@@ -566,14 +569,6 @@ RegionMatches(const char* s1, int s1off, const CharT* s2, int s2off, int count)
     return count == 0;
 }
 
-/* find UTC time from given date... no 1900 correction! */
-static double
-date_msecFromDate(double year, double mon, double mday, double hour,
-                  double min, double sec, double msec)
-{
-    return MakeDate(MakeDay(year, mon, mday), MakeTime(hour, min, sec, msec));
-}
-
 /* ES6 20.3.3.4. */
 static bool
 date_UTC(JSContext* cx, unsigned argc, Value* vp)
@@ -644,7 +639,8 @@ date_UTC(JSContext* cx, unsigned argc, Value* vp)
     }
 
     // Step 16.
-    args.rval().setDouble(TimeClip(MakeDate(MakeDay(yr, m, dt), MakeTime(h, min, s, milli))));
+    ClippedTime time = TimeClip(MakeDate(MakeDay(yr, m, dt), MakeTime(h, min, s, milli)));
+    args.rval().setDouble(time.value());
     return true;
 }
 
@@ -777,7 +773,7 @@ DaysInMonth(int year, int month)
  */
 template <typename CharT>
 static bool
-ParseISODate(const CharT* s, size_t length, double* result, DateTimeInfo* dtInfo)
+ParseISODate(const CharT* s, size_t length, ClippedTime* result, DateTimeInfo* dtInfo)
 {
     size_t i = 0;
     int tzMul = 1;
@@ -873,19 +869,16 @@ ParseISODate(const CharT* s, size_t length, double* result, DateTimeInfo* dtInfo
 
     month -= 1; /* convert month to 0-based */
 
-    double msec = date_msecFromDate(dateMul * double(year), month, day,
-                                    hour, min, sec, frac * 1000.0);
+    double msec = MakeDate(MakeDay(dateMul * double(year), month, day),
+                           MakeTime(hour, min, sec, frac * 1000.0));
 
     if (isLocalTime)
         msec = UTC(msec, dtInfo);
     else
         msec -= tzMul * (tzHour * msPerHour + tzMin * msPerMinute);
 
-    if (msec < -8.64e15 || msec > 8.64e15)
-        return false;
-
-    *result = msec;
-    return true;
+    *result = TimeClip(msec);
+    return NumbersAreIdentical(msec, result->value());
 
 #undef PEEK
 #undef NEED
@@ -895,7 +888,7 @@ ParseISODate(const CharT* s, size_t length, double* result, DateTimeInfo* dtInfo
 
 template <typename CharT>
 static bool
-ParseDate(const CharT* s, size_t length, double* result, DateTimeInfo* dtInfo)
+ParseDate(const CharT* s, size_t length, ClippedTime* result, DateTimeInfo* dtInfo)
 {
     if (ParseISODate(s, length, result, dtInfo))
         return true;
@@ -1157,19 +1150,19 @@ ParseDate(const CharT* s, size_t length, double* result, DateTimeInfo* dtInfo)
     if (hour < 0)
         hour = 0;
 
-    double msec = date_msecFromDate(year, mon, mday, hour, min, sec, 0);
+    double msec = MakeDate(MakeDay(year, mon, mday), MakeTime(hour, min, sec, 0));
 
     if (tzOffset == -1) /* no time zone specified, have to use local */
         msec = UTC(msec, dtInfo);
     else
         msec += tzOffset * msPerMinute;
 
-    *result = msec;
+    *result = TimeClip(msec);
     return true;
 }
 
 static bool
-ParseDate(JSLinearString* s, double* result, DateTimeInfo* dtInfo)
+ParseDate(JSLinearString* s, ClippedTime* result, DateTimeInfo* dtInfo)
 {
     AutoCheckCannotGC nogc;
     return s->hasLatin1Chars()
@@ -1194,45 +1187,44 @@ date_parse(JSContext* cx, unsigned argc, Value* vp)
     if (!linearStr)
         return false;
 
-    double result;
+    ClippedTime result;
     if (!ParseDate(linearStr, &result, &cx->runtime()->dateTimeInfo)) {
         args.rval().setNaN();
         return true;
     }
 
-    result = TimeClip(result);
-    args.rval().setNumber(result);
+    args.rval().setDouble(result.value());
     return true;
 }
 
-static inline double
+static ClippedTime
 NowAsMillis()
 {
-    return (double) (PRMJ_Now() / PRMJ_USEC_PER_MSEC);
+    return ClippedTime(static_cast<double>(PRMJ_Now()) / PRMJ_USEC_PER_MSEC);
 }
 
 bool
 js::date_now(JSContext* cx, unsigned argc, Value* vp)
 {
     CallArgs args = CallArgsFromVp(argc, vp);
-    args.rval().setDouble(NowAsMillis());
+    args.rval().setDouble(NowAsMillis().value());
     return true;
 }
 
 void
-DateObject::setUTCTime(double t)
+DateObject::setUTCTime(ClippedTime t)
 {
     for (size_t ind = COMPONENTS_START_SLOT; ind < RESERVED_SLOTS; ind++)
         setReservedSlot(ind, UndefinedValue());
 
-    setFixedSlot(UTC_TIME_SLOT, DoubleValue(t));
+    setFixedSlot(UTC_TIME_SLOT, DoubleValue(t.value()));
 }
 
 void
-DateObject::setUTCTime(double t, MutableHandleValue vp)
+DateObject::setUTCTime(ClippedTime t, MutableHandleValue vp)
 {
     setUTCTime(t);
-    vp.setDouble(t);
+    vp.setDouble(t.value());
 }
 
 void
@@ -1695,7 +1687,7 @@ date_setTime_impl(JSContext* cx, CallArgs args)
 {
     Rooted<DateObject*> dateObj(cx, &args.thisv().toObject().as<DateObject>());
     if (args.length() == 0) {
-        dateObj->setUTCTime(GenericNaN(), args.rval());
+        dateObj->setUTCTime(ClippedTime::NaN(), args.rval());
         return true;
     }
 
@@ -1760,7 +1752,7 @@ date_setMilliseconds_impl(JSContext* cx, CallArgs args)
     double time = MakeTime(HourFromTime(t), MinFromTime(t), SecFromTime(t), milli);
 
     /* Step 3. */
-    double u = TimeClip(UTC(MakeDate(Day(t), time), &cx->runtime()->dateTimeInfo));
+    ClippedTime u = TimeClip(UTC(MakeDate(Day(t), time), &cx->runtime()->dateTimeInfo));
 
     /* Steps 4-5. */
     dateObj->setUTCTime(u, args.rval());
@@ -1790,7 +1782,7 @@ date_setUTCMilliseconds_impl(JSContext* cx, CallArgs args)
     double time = MakeTime(HourFromTime(t), MinFromTime(t), SecFromTime(t), milli);
 
     /* Step 3. */
-    double v = TimeClip(MakeDate(Day(t), time));
+    ClippedTime v = TimeClip(MakeDate(Day(t), time));
 
     /* Steps 4-5. */
     dateObj->setUTCTime(v, args.rval());
@@ -1827,7 +1819,7 @@ date_setSeconds_impl(JSContext* cx, CallArgs args)
     double date = MakeDate(Day(t), MakeTime(HourFromTime(t), MinFromTime(t), s, milli));
 
     /* Step 5. */
-    double u = TimeClip(UTC(date, &cx->runtime()->dateTimeInfo));
+    ClippedTime u = TimeClip(UTC(date, &cx->runtime()->dateTimeInfo));
 
     /* Steps 6-7. */
     dateObj->setUTCTime(u, args.rval());
@@ -1864,7 +1856,7 @@ date_setUTCSeconds_impl(JSContext* cx, CallArgs args)
     double date = MakeDate(Day(t), MakeTime(HourFromTime(t), MinFromTime(t), s, milli));
 
     /* Step 5. */
-    double v = TimeClip(date);
+    ClippedTime v = TimeClip(date);
 
     /* Steps 6-7. */
     dateObj->setUTCTime(v, args.rval());
@@ -1906,7 +1898,7 @@ date_setMinutes_impl(JSContext* cx, CallArgs args)
     double date = MakeDate(Day(t), MakeTime(HourFromTime(t), m, s, milli));
 
     /* Step 6. */
-    double u = TimeClip(UTC(date, &cx->runtime()->dateTimeInfo));
+    ClippedTime u = TimeClip(UTC(date, &cx->runtime()->dateTimeInfo));
 
     /* Steps 7-8. */
     dateObj->setUTCTime(u, args.rval());
@@ -1948,7 +1940,7 @@ date_setUTCMinutes_impl(JSContext* cx, CallArgs args)
     double date = MakeDate(Day(t), MakeTime(HourFromTime(t), m, s, milli));
 
     /* Step 6. */
-    double v = TimeClip(date);
+    ClippedTime v = TimeClip(date);
 
     /* Steps 7-8. */
     dateObj->setUTCTime(v, args.rval());
@@ -1995,7 +1987,7 @@ date_setHours_impl(JSContext* cx, CallArgs args)
     double date = MakeDate(Day(t), MakeTime(h, m, s, milli));
 
     /* Step 6. */
-    double u = TimeClip(UTC(date, &cx->runtime()->dateTimeInfo));
+    ClippedTime u = TimeClip(UTC(date, &cx->runtime()->dateTimeInfo));
 
     /* Steps 7-8. */
     dateObj->setUTCTime(u, args.rval());
@@ -2042,7 +2034,7 @@ date_setUTCHours_impl(JSContext* cx, CallArgs args)
     double newDate = MakeDate(Day(t), MakeTime(h, m, s, milli));
 
     /* Step 7. */
-    double v = TimeClip(newDate);
+    ClippedTime v = TimeClip(newDate);
 
     /* Steps 8-9. */
     dateObj->setUTCTime(v, args.rval());
@@ -2074,7 +2066,7 @@ date_setDate_impl(JSContext* cx, CallArgs args)
     double newDate = MakeDate(MakeDay(YearFromTime(t), MonthFromTime(t), date), TimeWithinDay(t));
 
     /* Step 4. */
-    double u = TimeClip(UTC(newDate, &cx->runtime()->dateTimeInfo));
+    ClippedTime u = TimeClip(UTC(newDate, &cx->runtime()->dateTimeInfo));
 
     /* Steps 5-6. */
     dateObj->setUTCTime(u, args.rval());
@@ -2106,7 +2098,7 @@ date_setUTCDate_impl(JSContext* cx, CallArgs args)
     double newDate = MakeDate(MakeDay(YearFromTime(t), MonthFromTime(t), date), TimeWithinDay(t));
 
     /* Step 4. */
-    double v = TimeClip(newDate);
+    ClippedTime v = TimeClip(newDate);
 
     /* Steps 5-6. */
     dateObj->setUTCTime(v, args.rval());
@@ -2163,7 +2155,7 @@ date_setMonth_impl(JSContext* cx, CallArgs args)
     double newDate = MakeDate(MakeDay(YearFromTime(t), m, date), TimeWithinDay(t));
 
     /* Step 5. */
-    double u = TimeClip(UTC(newDate, &cx->runtime()->dateTimeInfo));
+    ClippedTime u = TimeClip(UTC(newDate, &cx->runtime()->dateTimeInfo));
 
     /* Steps 6-7. */
     dateObj->setUTCTime(u, args.rval());
@@ -2200,7 +2192,7 @@ date_setUTCMonth_impl(JSContext* cx, CallArgs args)
     double newDate = MakeDate(MakeDay(YearFromTime(t), m, date), TimeWithinDay(t));
 
     /* Step 5. */
-    double v = TimeClip(newDate);
+    ClippedTime v = TimeClip(newDate);
 
     /* Steps 6-7. */
     dateObj->setUTCTime(v, args.rval());
@@ -2258,7 +2250,7 @@ date_setFullYear_impl(JSContext* cx, CallArgs args)
     double newDate = MakeDate(MakeDay(y, m, date), TimeWithinDay(t));
 
     /* Step 6. */
-    double u = TimeClip(UTC(newDate, &cx->runtime()->dateTimeInfo));
+    ClippedTime u = TimeClip(UTC(newDate, &cx->runtime()->dateTimeInfo));
 
     /* Steps 7-8. */
     dateObj->setUTCTime(u, args.rval());
@@ -2300,7 +2292,7 @@ date_setUTCFullYear_impl(JSContext* cx, CallArgs args)
     double newDate = MakeDate(MakeDay(y, m, date), TimeWithinDay(t));
 
     /* Step 6. */
-    double v = TimeClip(newDate);
+    ClippedTime v = TimeClip(newDate);
 
     /* Steps 7-8. */
     dateObj->setUTCTime(v, args.rval());
@@ -2330,7 +2322,7 @@ date_setYear_impl(JSContext* cx, CallArgs args)
 
     /* Step 3. */
     if (IsNaN(y)) {
-        dateObj->setUTCTime(GenericNaN(), args.rval());
+        dateObj->setUTCTime(ClippedTime::NaN(), args.rval());
         return true;
     }
 
@@ -2374,7 +2366,7 @@ static const char * const months[] =
 static void
 print_gmt_string(char* buf, size_t size, double utctime)
 {
-    MOZ_ASSERT(TimeClip(utctime) == utctime);
+    MOZ_ASSERT(NumbersAreIdentical(TimeClip(utctime).value(), utctime));
     JS_snprintf(buf, size, "%s, %.2d %s %.4d %.2d:%.2d:%.2d GMT",
                 days[int(WeekDay(utctime))],
                 int(DateFromTime(utctime)),
@@ -2388,7 +2380,7 @@ print_gmt_string(char* buf, size_t size, double utctime)
 static void
 print_iso_string(char* buf, size_t size, double utctime)
 {
-    MOZ_ASSERT(TimeClip(utctime) == utctime);
+    MOZ_ASSERT(NumbersAreIdentical(TimeClip(utctime).value(), utctime));
     JS_snprintf(buf, size, "%.4d-%.2d-%.2dT%.2d:%.2d:%.2d.%.3dZ",
                 int(YearFromTime(utctime)),
                 int(MonthFromTime(utctime)) + 1,
@@ -2402,7 +2394,7 @@ print_iso_string(char* buf, size_t size, double utctime)
 static void
 print_iso_extended_string(char* buf, size_t size, double utctime)
 {
-    MOZ_ASSERT(TimeClip(utctime) == utctime);
+    MOZ_ASSERT(NumbersAreIdentical(TimeClip(utctime).value(), utctime));
     JS_snprintf(buf, size, "%+.6d-%.2d-%.2dT%.2d:%.2d:%.2d.%.3dZ",
                 int(YearFromTime(utctime)),
                 int(MonthFromTime(utctime)) + 1,
@@ -2558,7 +2550,7 @@ date_format(JSContext* cx, double date, formatspec format, MutableHandleValue rv
     if (!IsFinite(date)) {
         JS_snprintf(buf, sizeof buf, js_NaN_date_str);
     } else {
-        MOZ_ASSERT(TimeClip(date) == date);
+        MOZ_ASSERT(NumbersAreIdentical(TimeClip(date).value(), date));
 
         double local = LocalTime(date, &cx->runtime()->dateTimeInfo);
 
@@ -2973,9 +2965,9 @@ static const JSFunctionSpec date_methods[] = {
 };
 
 static bool
-NewDateObject(JSContext* cx, const CallArgs& args, double d)
+NewDateObject(JSContext* cx, const CallArgs& args, ClippedTime t)
 {
-    JSObject* obj = NewDateObjectMsec(cx, d);
+    JSObject* obj = NewDateObjectMsec(cx, t);
     if (!obj)
         return false;
 
@@ -2984,9 +2976,9 @@ NewDateObject(JSContext* cx, const CallArgs& args, double d)
 }
 
 static bool
-ToDateString(JSContext* cx, const CallArgs& args, double d)
+ToDateString(JSContext* cx, const CallArgs& args, ClippedTime t)
 {
-    return date_format(cx, d, FORMATSPEC_FULL, args.rval());
+    return date_format(cx, t.value(), FORMATSPEC_FULL, args.rval());
 }
 
 static bool
@@ -2994,7 +2986,7 @@ DateNoArguments(JSContext* cx, const CallArgs& args)
 {
     MOZ_ASSERT(args.length() == 0);
 
-    double now = NowAsMillis();
+    ClippedTime now = NowAsMillis();
 
     if (args.isConstructing())
         return NewDateObject(cx, args, now);
@@ -3008,7 +3000,7 @@ DateOneArgument(JSContext* cx, const CallArgs& args)
     MOZ_ASSERT(args.length() == 1);
 
     if (args.isConstructing()) {
-        double d;
+        ClippedTime t;
 
         if (!ToPrimitive(cx, args[0]))
             return false;
@@ -3018,17 +3010,16 @@ DateOneArgument(JSContext* cx, const CallArgs& args)
             if (!linearStr)
                 return false;
 
-            if (!ParseDate(linearStr, &d, &cx->runtime()->dateTimeInfo))
-                d = GenericNaN();
-            else
-                d = TimeClip(d);
+            if (!ParseDate(linearStr, &t, &cx->runtime()->dateTimeInfo))
+                t = ClippedTime::NaN();
         } else {
+            double d;
             if (!ToNumber(cx, args[0], &d))
                 return false;
-            d = TimeClip(d);
+            t = TimeClip(d);
         }
 
-        return NewDateObject(cx, args, d);
+        return NewDateObject(cx, args, t);
     }
 
     return ToDateString(cx, args, NowAsMillis());
@@ -3131,7 +3122,7 @@ js::DateConstructor(JSContext* cx, unsigned argc, Value* vp)
 static bool
 FinishDateClassInit(JSContext* cx, HandleObject ctor, HandleObject proto)
 {
-    proto->as<DateObject>().setUTCTime(GenericNaN());
+    proto->as<DateObject>().setUTCTime(ClippedTime::NaN());
 
     /*
      * Date.prototype.toGMTString has the same initial value as
@@ -3173,13 +3164,13 @@ const Class DateObject::class_ = {
     }
 };
 
-JS_FRIEND_API(JSObject*)
-js::NewDateObjectMsec(JSContext* cx, double msec_time)
+JSObject*
+js::NewDateObjectMsec(JSContext* cx, ClippedTime t)
 {
     JSObject* obj = NewBuiltinClassInstance(cx, &DateObject::class_);
     if (!obj)
         return nullptr;
-    obj->as<DateObject>().setUTCTime(msec_time);
+    obj->as<DateObject>().setUTCTime(t);
     return obj;
 }
 
@@ -3188,8 +3179,8 @@ js::NewDateObject(JSContext* cx, int year, int mon, int mday,
                   int hour, int min, int sec)
 {
     MOZ_ASSERT(mon < 12);
-    double msec_time = date_msecFromDate(year, mon, mday, hour, min, sec, 0);
-    return NewDateObjectMsec(cx, UTC(msec_time, &cx->runtime()->dateTimeInfo));
+    double msec_time = MakeDate(MakeDay(year, mon, mday), MakeTime(hour, min, sec, 0.0));
+    return NewDateObjectMsec(cx, TimeClip(UTC(msec_time, &cx->runtime()->dateTimeInfo)));
 }
 
 JS_FRIEND_API(bool)
diff --git a/js/src/jsdate.h b/js/src/jsdate.h
index 29fcf8c88a56..29bde83bb237 100644
--- a/js/src/jsdate.h
+++ b/js/src/jsdate.h
@@ -13,9 +13,12 @@
 
 #include "jstypes.h"
 
+#include "js/Date.h"
 #include "js/RootingAPI.h"
 #include "js/TypeDecls.h"
 
+#include "vm/DateTime.h"
+
 namespace js {
 
 /*
@@ -26,8 +29,8 @@ namespace js {
  * Construct a new Date Object from a time value given in milliseconds UTC
  * since the epoch.
  */
-extern JS_FRIEND_API(JSObject*)
-NewDateObjectMsec(JSContext* cx, double msec_time);
+extern JSObject*
+NewDateObjectMsec(JSContext* cx, JS::ClippedTime t);
 
 /*
  * Construct a new Date Object from an exploded local time value.
diff --git a/js/src/vm/DateObject.h b/js/src/vm/DateObject.h
index cfe1a545ddbb..e15b3c69ff4f 100644
--- a/js/src/vm/DateObject.h
+++ b/js/src/vm/DateObject.h
@@ -9,6 +9,7 @@
 
 #include "jsobj.h"
 
+#include "js/Date.h"
 #include "js/Value.h"
 
 namespace js {
@@ -46,8 +47,8 @@ class DateObject : public NativeObject
     }
 
     // Set UTC time to a given time and invalidate cached local time.
-    void setUTCTime(double t);
-    void setUTCTime(double t, MutableHandleValue vp);
+    void setUTCTime(JS::ClippedTime t);
+    void setUTCTime(JS::ClippedTime t, MutableHandleValue vp);
 
     inline double cachedLocalTime(DateTimeInfo* dtInfo);
 
diff --git a/js/src/vm/DateTime.h b/js/src/vm/DateTime.h
index 4b00a6423439..4ec477b3ee61 100644
--- a/js/src/vm/DateTime.h
+++ b/js/src/vm/DateTime.h
@@ -39,19 +39,6 @@ const unsigned SecondsPerDay = SecondsPerHour * 24;
 
 const double StartOfTime = -8.64e15;
 const double EndOfTime = 8.64e15;
-const double MaxTimeMagnitude = 8.64e15;
-
-/* ES5 15.9.1.14. */
-inline double
-TimeClip(double time)
-{
-    /* Steps 1-2. */
-    if (!mozilla::IsFinite(time) || mozilla::Abs(time) > MaxTimeMagnitude)
-        return JS::GenericNaN();
-
-    /* Step 3. */
-    return JS::ToInteger(time + (+0.0));
-}
 
 /*
  * Stores date/time information, particularly concerning the current local
diff --git a/js/src/vm/StructuredClone.cpp b/js/src/vm/StructuredClone.cpp
index 785496a9e617..7e106834345a 100644
--- a/js/src/vm/StructuredClone.cpp
+++ b/js/src/vm/StructuredClone.cpp
@@ -40,6 +40,7 @@
 #include "jswrapper.h"
 
 #include "builtin/MapObject.h"
+#include "js/Date.h"
 #include "vm/SharedArrayObject.h"
 #include "vm/TypedArrayObject.h"
 #include "vm/WrapperObject.h"
@@ -53,6 +54,7 @@ using mozilla::BitwiseCast;
 using mozilla::IsNaN;
 using mozilla::LittleEndian;
 using mozilla::NativeEndian;
+using mozilla::NumbersAreIdentical;
 using JS::CanonicalizeNaN;
 
 // When you make updates here, make sure you consider whether you need to bump the
@@ -1591,12 +1593,13 @@ JSStructuredCloneReader::startRead(MutableHandleValue vp)
         double d;
         if (!in.readDouble(&d) || !checkDouble(d))
             return false;
-        if (!IsNaN(d) && d != TimeClip(d)) {
+        JS::ClippedTime t = JS::TimeClip(d);
+        if (!NumbersAreIdentical(d, t.value())) {
             JS_ReportErrorNumber(context(), GetErrorMessage, nullptr,
                                  JSMSG_SC_BAD_SERIALIZED_DATA, "date");
             return false;
         }
-        JSObject* obj = NewDateObjectMsec(context(), d);
+        JSObject* obj = NewDateObjectMsec(context(), t);
         if (!obj)
             return false;
         vp.setObject(*obj);