diff --git a/js/src/jsdate.cpp b/js/src/jsdate.cpp
index 07af3d1..ff8fd6c 100644
--- a/js/src/jsdate.cpp
+++ b/js/src/jsdate.cpp
@@ -2353,12 +2353,15 @@ static PRMJTime ToPRMJTime(double localTime, double utcTime) {
 static size_t FormatTime(char* buf, int buflen, const char* fmt, double utcTime,
                          double localTime) {
   PRMJTime prtm = ToPRMJTime(localTime, utcTime);
-  int eqivalentYear = IsRepresentableAsTime32(utcTime)
-                          ? prtm.tm_year
-                          : EquivalentYearForDST(prtm.tm_year);
+  // If an equivalent year was used to compute the date/time components, use
+  // the same equivalent year to determine the time zone name and offset in
+  // PRMJ_FormatTime(...).
+  int timeZoneYear = IsRepresentableAsTime32(utcTime)
+                     ? prtm.tm_year
+                     : EquivalentYearForDST(prtm.tm_year);
   int offsetInSeconds = (int)floor((localTime - utcTime) / msPerSecond);
 
-  return PRMJ_FormatTime(buf, buflen, fmt, &prtm, eqivalentYear,
+  return PRMJ_FormatTime(buf, buflen, fmt, &prtm, timeZoneYear,
                          offsetInSeconds);
 }
 
diff --git a/js/src/vm/Time.cpp b/js/src/vm/Time.cpp
index f59977f..5ee4794 100644
--- a/js/src/vm/Time.cpp
+++ b/js/src/vm/Time.cpp
@@ -247,7 +247,7 @@ static void PRMJ_InvalidParameterHandler(const wchar_t* expression,
 
 /* Format a time value into a buffer. Same semantics as strftime() */
 size_t PRMJ_FormatTime(char* buf, int buflen, const char* fmt,
-                       const PRMJTime* prtm, int equivalentYear,
+                       const PRMJTime* prtm, int timeZoneYear,
                        int offsetInSeconds) {
   size_t result = 0;
 #if defined(XP_UNIX) || defined(XP_WIN)
@@ -280,7 +280,8 @@ size_t PRMJ_FormatTime(char* buf, int buflen, const char* fmt,
      * Fill out |td| to the time represented by |prtm|, leaving the
      * timezone fields zeroed out. localtime_r will then fill in the
      * timezone fields for that local time according to the system's
-     * timezone parameters.
+     * timezone parameters. Use |timeZoneYear| for the year to ensure the
+     * time zone name matches the time zone offset used by the caller.
      */
     struct tm td;
     memset(&td, 0, sizeof(td));
@@ -290,19 +291,12 @@ size_t PRMJ_FormatTime(char* buf, int buflen, const char* fmt,
     td.tm_mday = prtm->tm_mday;
     td.tm_mon = prtm->tm_mon;
     td.tm_wday = prtm->tm_wday;
-    td.tm_year = prtm->tm_year - 1900;
+    td.tm_year = timeZoneYear - 1900;
     td.tm_yday = prtm->tm_yday;
     td.tm_isdst = prtm->tm_isdst;
 
     time_t t = mktime(&td);
 
-    // If |prtm| cannot be represented in |time_t| the year is probably
-    // out of range, try again with the DST equivalent year.
-    if (t == static_cast<time_t>(-1)) {
-      td.tm_year = equivalentYear - 1900;
-      t = mktime(&td);
-    }
-
     // If either mktime or localtime_r failed, fill in the fallback time
     // zone offset |offsetInSeconds| and set the time zone identifier to
     // the empty string.
diff --git a/js/src/vm/Time.h b/js/src/vm/Time.h
index 3a51d86..37b7fae 100644
--- a/js/src/vm/Time.h
+++ b/js/src/vm/Time.h
@@ -49,7 +49,7 @@ inline void PRMJ_NowShutdown() {}
 
 /* Format a time value into a buffer. Same semantics as strftime() */
 extern size_t PRMJ_FormatTime(char* buf, int buflen, const char* fmt,
-                              const PRMJTime* tm, int equivalentYear,
+                              const PRMJTime* tm, int timeZoneYear,
                               int offsetInSeconds);
 
 /**