diff --git a/lib/Date/Format/Generic.pm b/lib/Date/Format/Generic.pm
index b3b8bdf..7387619 100644
--- a/lib/Date/Format/Generic.pm
+++ b/lib/Date/Format/Generic.pm
@@ -252,12 +252,17 @@ sub format_V {
     # Day-of-year of the Thursday in this ISO week
     my $thu = $yday - $mwday + 3;
     if ($thu < 0) {
-        # Thursday falls in the previous year
+        # Thursday falls in the previous year — this date belongs to
+        # the last ISO week of the previous year, skip year-end check
         my $py = $year - 1;
         $thu += (($py % 4 == 0 && $py % 100 != 0) || $py % 400 == 0) ? 366 : 365;
     }
-    my $ylen = (($year % 4 == 0 && $year % 100 != 0) || $year % 400 == 0) ? 366 : 365;
-    return sprintf("%02d", 1) if $thu >= $ylen;
+    else {
+        # Thursday falls in the next year — this date belongs to
+        # ISO week 1 of the following year
+        my $ylen = (($year % 4 == 0 && $year % 100 != 0) || $year % 400 == 0) ? 366 : 365;
+        return sprintf("%02d", 1) if $thu >= $ylen;
+    }
     sprintf("%02d", int($thu / 7) + 1);
 }
 
diff --git a/t/iso-week-number.t b/t/iso-week-number.t
index a683d73..c26d8b3 100644
--- a/t/iso-week-number.t
+++ b/t/iso-week-number.t
@@ -43,6 +43,18 @@ my @cases = (
     [timegm(0,0,0,27,11,104), "53", "2004-12-27 (Mon) is week 53"],
     [timegm(0,0,0, 2,0,105),  "53", "2005-01-02 (Sun) is week 53 of 2004"],
     [timegm(0,0,0, 3,0,105),  "01", "2005-01-03 (Mon) is week 01 of 2005"],
+
+    # 2021: Jan 1 is Friday, previous year (2020) is leap year
+    # This is a regression test: the leap-year adjustment pushed $thu to
+    # exactly equal the current year's day count, triggering the year-end
+    # check incorrectly and returning week 01 instead of 53.
+    [timegm(0,0,0, 1,0,121), "53", "2021-01-01 (Fri) is week 53 of 2020 (leap year boundary)"],
+    [timegm(0,0,0, 2,0,121), "53", "2021-01-02 (Sat) is week 53 of 2020"],
+    [timegm(0,0,0, 3,0,121), "53", "2021-01-03 (Sun) is week 53 of 2020"],
+    [timegm(0,0,0, 4,0,121), "01", "2021-01-04 (Mon) is week 01 of 2021"],
+
+    # 2017: Jan 1 is Sunday → week 52 of 2016 (2016 is leap year)
+    [timegm(0,0,0, 1,0,117), "52", "2017-01-01 (Sun) is week 52 of 2016 (leap year)"],
 );
 
 for my $case (@cases) {