diff --git a/js/ui/dateMenu.js b/js/ui/dateMenu.js
index 60f5bdc45..79b1ce3dd 100644
--- a/js/ui/dateMenu.js
+++ b/js/ui/dateMenu.js
@@ -573,6 +573,11 @@ var DateMenuButton = new Lang.Class({
         // https://bugzilla.gnome.org/show_bug.cgi?id=678507
         System.clearDateCaches();
 
+        // To reduce the number of times that Shell opens /etc/localtime on
+        // the main thread to parse timezone info, we cache the result. That
+        // needs to be cleared when we change timezones.
+        Shell.util_clear_timezone_cache();
+
         this._calendar.updateTimeZone();
     },
 
diff --git a/js/ui/environment.js b/js/ui/environment.js
index 719680f61..a2a15a599 100644
--- a/js/ui/environment.js
+++ b/js/ui/environment.js
@@ -118,7 +118,7 @@ function init() {
 
     // Work around https://bugzilla.mozilla.org/show_bug.cgi?id=508783
     Date.prototype.toLocaleFormat = function(format) {
-        return Shell.util_format_date(format, this.getTime());
+        return Shell.util_format_now(format);
     };
 
     let slowdownEnv = GLib.getenv('GNOME_SHELL_SLOWDOWN_FACTOR');
diff --git a/src/shell-util.c b/src/shell-util.c
index 70b8c0611..76526126f 100644
--- a/src/shell-util.c
+++ b/src/shell-util.c
@@ -20,6 +20,8 @@
 #include <langinfo.h>
 #endif
 
+static GTimeZone *local_tz;
+
 static void
 stop_pick (ClutterActor       *actor,
            const ClutterColor *color)
@@ -154,6 +156,30 @@ shell_util_format_date (const char *format,
   return result;
 }
 
+char *
+shell_util_format_now (const char *format)
+{
+  GDateTime *datetime;
+  char *ret;
+
+  if (local_tz == NULL)
+    local_tz = g_time_zone_new_local ();
+
+  datetime = g_date_time_new_now (local_tz);
+  if (!datetime)
+    return g_strdup ("");
+
+  ret = g_date_time_format (datetime, format);
+  g_date_time_unref (datetime);
+  return ret;
+}
+
+void
+shell_util_clear_timezone_cache (void)
+{
+  g_clear_pointer (&local_tz, g_time_zone_unref);
+}
+
 /**
  * shell_util_get_week_start:
  *
diff --git a/src/shell-util.h b/src/shell-util.h
index 2218594c1..8b31c9eb7 100644
--- a/src/shell-util.h
+++ b/src/shell-util.h
@@ -22,6 +22,8 @@ int      shell_util_get_week_start             (void);
 
 char    *shell_util_format_date                (const char       *format,
                                                 gint64            time_ms);
+char    *shell_util_format_now                 (const char       *format);
+void     shell_util_clear_timezone_cache       (void);
 const char *shell_util_translate_time_string   (const char *str);
 
 char    *shell_util_regex_escape               (const char *str);