diff --git a/tests/c/diff.cpp b/tests/c/diff.cpp
index b4cfbbc..77c9b1a 100644
--- a/tests/c/diff.cpp
+++ b/tests/c/diff.cpp
@@ -428,3 +428,54 @@ TEST(timelib_diff, test_time_fall_type2_stsec_type2_dtsec)
 	test_parse("America/New_York", "2010-11-07 01:00:00 EST", "2010-11-07 01:59:59 EDT");
 	CHECKDIFF(0, 0, 0, 0, 0, 1, 0);
 }
+
+
+TEST(timelib_diff, php_gh13857a)
+{
+	test_parse("Asia/Tokyo", "UTC", "2024-04-01 00:49:22", "2024-03-31 23:48:22");
+	CHECKDIFF(0, 0, 0, 7, 59, 0, 0);
+}
+
+TEST(timelib_diff, php_gh13857b)
+{
+	test_parse("Asia/Tokyo", "UTC", "2024-01-01 00:49:22", "2023-12-31 23:48:22");
+	CHECKDIFF(0, 0, 0, 7, 59, 0, 0);
+}
+
+TEST(timelib_diff, php_gh13857c)
+{
+	test_parse("Asia/Tokyo", "UTC", "2023-12-01 00:49:22", "2023-11-30 23:48:22");
+	CHECKDIFF(0, 0, 0, 7, 59, 0, 0);
+}
+
+TEST(timelib_diff, php_gh13857d)
+{
+	test_parse("Asia/Tokyo", "UTC", "2024-02-01 00:49:22", "2024-01-31 23:48:22");
+	CHECKDIFF(0, 0, 0, 7, 59, 0, 0);
+}
+
+
+TEST(timelib_diff, php_gh13857e)
+{
+	test_parse("UTC", "Asia/Tokyo", "2024-03-31 23:48:22", "2024-04-01 00:49:22");
+	CHECKDIFF(0, 0, 0, 7, 59, 0, 0);
+}
+
+TEST(timelib_diff, php_gh13857f)
+{
+	test_parse("UTC", "Asia/Tokyo", "2023-12-31 23:48:22", "2024-01-01 00:49:22");
+	CHECKDIFF(0, 0, 0, 7, 59, 0, 0);
+}
+
+TEST(timelib_diff, php_gh13857g)
+{
+	test_parse("UTC", "Asia/Tokyo", "2023-11-30 23:48:22", "2023-12-01 00:49:22");
+	CHECKDIFF(0, 0, 0, 7, 59, 0, 0);
+}
+
+TEST(timelib_diff, php_gh13857h)
+{
+	test_parse("UTC", "Asia/Tokyo", "2024-01-31 23:48:22", "2024-02-01 00:49:22");
+	CHECKDIFF(0, 0, 0, 7, 59, 0, 0);
+}
+
diff --git a/tm2unixtime.c b/tm2unixtime.c
index f13a941..b35eb70 100644
--- a/tm2unixtime.c
+++ b/tm2unixtime.c
@@ -81,7 +81,20 @@ static void do_range_limit_days_relative(timelib_sll *base_y, timelib_sll *base_
 /*
 	printf( "S: Y%d M%d   %d %d %d   %d\n", year, month, *y, *m, *d, days);
 */
+	if (*y == -1 && *m == 11 && *d == 31) {
+		(*y) = 0;
+		(*m) = 0;
+		(*d) = 0;
+	}
 	if (!invert) {
+		if (*m == -1) {
+			leapyear = timelib_is_leap(year);
+			days = leapyear ? days_in_month_leap[month] : days_in_month[month];
+			if (*d >= days) {
+				*d -= days;
+				(*m)++;
+			}
+		}
 		while (*d < 0) {
 			dec_month(&year, &month);
 			leapyear = timelib_is_leap(year);
@@ -93,6 +106,14 @@ static void do_range_limit_days_relative(timelib_sll *base_y, timelib_sll *base_
 			(*m)--;
 		}
 	} else {
+		if (*m == -1 && month > 1) {
+			leapyear = timelib_is_leap(year);
+			days = leapyear ? days_in_month_leap[month + *m] : days_in_month[month + *m];
+			if (*d >= days) {
+				*d -= days;
+				(*m)++;
+			}
+		}
 		while (*d < 0) {
 			leapyear = timelib_is_leap(year);
 			days = leapyear ? days_in_month_leap[month] : days_in_month[month];
@@ -191,7 +212,6 @@ void timelib_do_rel_normalize(timelib_time *base, timelib_rel_time *rt)
 	do_range_limit(0, 60, 60, &rt->s, &rt->i);
 	do_range_limit(0, 60, 60, &rt->i, &rt->h);
 	do_range_limit(0, 24, 24, &rt->h, &rt->d);
-	do_range_limit(0, 12, 12, &rt->m, &rt->y);
 
 	do_range_limit_days_relative(&base->y, &base->m, &rt->y, &rt->m, &rt->d, rt->invert);
 	do_range_limit(0, 12, 12, &rt->m, &rt->y);