diff --git a/src/calibre/utils/iso8601.py b/src/calibre/utils/iso8601.py
index a425056f45..93f9cedb98 100644
--- a/src/calibre/utils/iso8601.py
+++ b/src/calibre/utils/iso8601.py
@@ -5,8 +5,6 @@
 from __future__ import (unicode_literals, division, absolute_import,
                         print_function)
 from datetime import datetime
-from decimal import Decimal
-import re
 
 from dateutil.tz import tzlocal, tzutc, tzoffset
 
@@ -31,132 +29,22 @@ local_tz = SafeLocalTimeZone()
 del tzutc, tzlocal
 UNDEFINED_DATE = datetime(101,1,1, tzinfo=utc_tz)
 
-if hasattr(speedup, 'parse_iso8601'):  # For people running from source without updated binaries
-    def parse_iso8601(date_string, assume_utc=False, as_utc=True):
-        if not date_string:
-            return UNDEFINED_DATE
-        dt, aware, tzseconds = speedup.parse_iso8601(date_string)
-        tz = utc_tz if assume_utc else local_tz
-        if aware:  # timezone was specified
-            if tzseconds == 0:
-                tz = utc_tz
-            else:
-                sign = '-' if tzseconds < 0 else '+'
-                description = "%s%02d:%02d" % (sign, abs(tzseconds) // 3600, (abs(tzseconds) % 3600) // 60)
-                tz = tzoffset(description, tzseconds)
-        dt = dt.replace(tzinfo=tz)
-        if as_utc and tz is utc_tz:
-            return dt
-        return dt.astimezone(utc_tz if as_utc else local_tz)
-else:
-    # Pure python implementation
-    _iso_pat = None
-
-    def iso_pat():
-        global _iso_pat
-        if _iso_pat is None:
-            _iso_pat = re.compile(
-            # Adapted from http://delete.me.uk/2005/03/iso8601.html
-            r"""
-            (?P<year>[0-9]{4})
-            (
-                (
-                    (-(?P<monthdash>[0-9]{1,2}))
-                    |
-                    (?P<month>[0-9]{2})
-                    (?!$)  # Don't allow YYYYMM
-                )
-                (
-                    (
-                        (-(?P<daydash>[0-9]{1,2}))
-                        |
-                        (?P<day>[0-9]{2})
-                    )
-                    (
-                        (
-                            (?P<separator>[ T])
-                            (?P<hour>[0-9]{2})
-                            (:{0,1}(?P<minute>[0-9]{2})){0,1}
-                            (
-                                :{0,1}(?P<second>[0-9]{1,2})
-                                ([.,](?P<second_fraction>[0-9]+)){0,1}
-                            ){0,1}
-                            (?P<timezone>
-                                Z
-                                |
-                                (
-                                    (?P<tz_sign>[-+])
-                                    (?P<tz_hour>[0-9]{2})
-                                    :{0,1}
-                                    (?P<tz_minute>[0-9]{2}){0,1}
-                                )
-                            ){0,1}
-                        ){0,1}
-                    )
-                ){0,1}  # YYYY-MM
-            ){0,1}  # YYYY only
-            $
-            """, re.VERBOSE)
-        return _iso_pat
-
-    def to_int(d, key, default_to_zero=False, default=None, required=True):
-        """Pull a value from the dict and convert to int
-
-        :param default_to_zero: If the value is None or empty, treat it as zero
-        :param default: If the value is missing in the dict use this default
-
-        """
-        value = d.get(key) or default
-        if (value is None or value == '') and default_to_zero:
-            return 0
-        if value is None:
-            if required:
-                raise ValueError("Unable to read %s from %s" % (key, d))
+def parse_iso8601(date_string, assume_utc=False, as_utc=True):
+    if not date_string:
+        return UNDEFINED_DATE
+    dt, aware, tzseconds = speedup.parse_iso8601(date_string)
+    tz = utc_tz if assume_utc else local_tz
+    if aware:  # timezone was specified
+        if tzseconds == 0:
+            tz = utc_tz
         else:
-            return int(value)
-
-    def parse_timezone(matches, default_timezone=utc_tz):
-        """Parses ISO 8601 time zone specs into tzinfo offsets
-
-        """
-
-        if matches["timezone"] == "Z":
-            return utc_tz
-        # This isn't strictly correct, but it's common to encounter dates without
-        # timezones so I'll assume the default (which defaults to UTC).
-        # Addresses issue 4.
-        if matches["timezone"] is None:
-            return default_timezone
-        sign = matches["tz_sign"]
-        hours = to_int(matches, "tz_hour")
-        minutes = to_int(matches, "tz_minute", default_to_zero=True)
-        description = "%s%02d:%02d" % (sign, hours, minutes)
-        if sign == "-":
-            hours = -hours
-            minutes = -minutes
-        return tzoffset(description, 3600*hours + 60*minutes)
-
-    def parse_iso8601(date_string, assume_utc=False, as_utc=True):
-        if not date_string:
-            return UNDEFINED_DATE
-        if isinstance(date_string, bytes):
-            date_string = date_string.decode('ascii')
-        m = iso_pat().match(date_string)
-        if m is None:
-            raise ValueError('%r is not a valid ISO8601 date' % date_string)
-        groups = m.groupdict()
-        tz = parse_timezone(groups, default_timezone=utc_tz if assume_utc else local_tz)
-        groups["second_fraction"] = int(Decimal("0.%s" % (groups["second_fraction"] or 0)) * Decimal("1000000.0"))
-        return datetime(
-                year=to_int(groups, "year"),
-                month=to_int(groups, "month", default=to_int(groups, "monthdash", required=False, default=1)),
-                day=to_int(groups, "day", default=to_int(groups, "daydash", required=False, default=1)),
-                hour=to_int(groups, "hour", default_to_zero=True),
-                minute=to_int(groups, "minute", default_to_zero=True),
-                second=to_int(groups, "second", default_to_zero=True),
-                microsecond=groups["second_fraction"],
-                tzinfo=tz,
-        ).astimezone(utc_tz if as_utc else local_tz)
+            sign = '-' if tzseconds < 0 else '+'
+            description = "%s%02d:%02d" % (sign, abs(tzseconds) // 3600, (abs(tzseconds) % 3600) // 60)
+            tz = tzoffset(description, tzseconds)
+    dt = dt.replace(tzinfo=tz)
+    if as_utc and tz is utc_tz:
+        return dt
+    return dt.astimezone(utc_tz if as_utc else local_tz)
 
 if __name__ == '__main__':
     import sys