diff --git a/i3pystatus/clock.py b/i3pystatus/clock.py
index 61c9de4..33df881 100644
--- a/i3pystatus/clock.py
+++ b/i3pystatus/clock.py
@@ -3,7 +3,7 @@
 
 import os
 import locale
-import datetime
+import time
 
 from i3pystatus import IntervalModule
 
@@ -45,7 +45,7 @@ class Clock(IntervalModule):
             lang = (None, None)
 
         if lang != locale.getlocale(locale.LC_TIME):
-            # affects datetime.time.strftime() in whole program
+            # affects time.strftime() in whole program
             locale.setlocale(locale.LC_TIME, lang)
 
         if self.format is None:
@@ -65,32 +65,26 @@ class Clock(IntervalModule):
     def expand_formats(formats):
         def expand_format(format_):
             if isinstance(format_, tuple):
-                return (format_[0], format_[1] if len(format_) > 1 else None)
-            return (format_, None)
+                # check if timezone exists (man tzset)
+                if len(format_) > 1 and os.path.isfile('/usr/share/zoneinfo/' + format_[1]):
+                    return (format_[0], format_[1])
+                else:
+                    return (format_[0], time.tzname[0])
+            return (format_, time.tzname[0])
 
         return [expand_format(format_) for format_ in formats]
 
     def run(self):
-        # Safest way is to work from utc and localize afterwards
-        if self.format[self.current_format_id][1]:
-            try:
-                import pytz
-            except ImportError as e:
-                raise RuntimeError("Need pytz for timezones") from e
-            utc_dt = pytz.utc.localize(datetime.datetime.utcnow())
-            tz = pytz.timezone(self.format[self.current_format_id][1])
-            dt = tz.normalize(utc_dt.astimezone(tz))
-        else:
-            dt = datetime.datetime.now()
-
-        output = dt.strftime(self.format[self.current_format_id][0])
+        # set correct timezone
+        if time.tzname[0] is not self.format[self.current_format_id][1]:
+            os.environ.putenv('TZ', self.format[self.current_format_id][1])
+            time.tzset()
 
         self.output = {
-            "full_text": output,
+            "full_text": time.strftime(self.format[self.current_format_id][0]),
+            "color": self.color,
             "urgent": False,
         }
-        if self.color != "i3Bar":
-            self.output["color"] = self.color
 
     def scroll_format(self, step=1):
         self.current_format_id = (self.current_format_id + step) % len(self.format)