diff --git a/lib/Date/Format/Generic.pm b/lib/Date/Format/Generic.pm
index b3b8bdf..8eca006 100644
--- a/lib/Date/Format/Generic.pm
+++ b/lib/Date/Format/Generic.pm
@@ -92,7 +92,7 @@ sub time2str
   {
    @$me = localtime($time);
   }
- $me->[9] = $time;
+ $me->[9] = $epoch;
  _subs($me,$fmt);
 }
 
diff --git a/t/time2str-tz-epoch.t b/t/time2str-tz-epoch.t
new file mode 100644
index 0000000..64146d0
--- /dev/null
+++ b/t/time2str-tz-epoch.t
@@ -0,0 +1,43 @@
+use strict;
+use warnings;
+use Test::More;
+use Date::Format qw(time2str);
+use Time::Local qw(timegm);
+
+# Regression: time2str stored tz-adjusted epoch in $me->[9] instead of
+# the real epoch.  This caused format_G (GPS week) to give wrong results
+# when a non-UTC timezone was specified and the epoch was near a GPS week
+# boundary.  format_z was also affected (DST lookup used wrong time).
+
+my $gps_epoch = 315964800;  # midnight UTC, Jan 6, 1980
+
+# GPS week 1 starts exactly 604800s after GPS epoch
+my $week1_start = $gps_epoch + 604800;  # midnight UTC, Jan 13, 1980
+
+# Without timezone: both should agree on the week boundary
+is(time2str("%G", $week1_start, "UTC"), "1",
+    "week 1 start with UTC");
+
+# With EST (-5h): the real epoch hasn't changed, so GPS week must be the same.
+# Before the fix, $me->[9] was epoch+offset, making format_G compute
+# int((epoch-18000 - gps_epoch) / 604800) = 0 instead of 1.
+is(time2str("%G", $week1_start, "EST"), "1",
+    "week 1 start with EST — GPS week must match UTC");
+
+# Edge case: one second before week 1
+is(time2str("%G", $week1_start - 1, "EST"), "0",
+    "one second before week 1, EST — still week 0");
+
+# A date well within a week should be unaffected by timezone
+my $mid_week = $gps_epoch + 604800 * 100 + 43200;  # week 100, noon UTC
+is(time2str("%G", $mid_week, "UTC"), "100", "mid-week UTC");
+is(time2str("%G", $mid_week, "EST"), "100", "mid-week EST");
+is(time2str("%G", $mid_week, "JST"), "100", "mid-week JST (+9)");
+
+# format_s (%s) should always return the real epoch regardless of timezone
+is(time2str("%s", $week1_start, "UTC"), "$week1_start",
+    "%s with UTC returns real epoch");
+is(time2str("%s", $week1_start, "EST"), "$week1_start",
+    "%s with EST returns real epoch (not adjusted)");
+
+done_testing;