diff --git a/vlib/time/custom_format_test.v b/vlib/time/custom_format_test.v
index de6bf26c84..3447030875 100644
--- a/vlib/time/custom_format_test.v
+++ b/vlib/time/custom_format_test.v
@@ -36,3 +36,9 @@ fn test_hours() {
 	assert time.parse('2023-08-04 22:00:45')!.custom_format('ii A i a hh A h a') == '10 PM 10 pm 10 PM 10 pm'
 	assert time.parse('2023-08-04 23:00:45')!.custom_format('ii A i a hh A h a') == '11 PM 11 pm 11 PM 11 pm'
 }
+
+fn test_zero_date() {
+	zero_date := time.Time{}
+	res := zero_date.custom_format('M MM Mo MMM MMMM |1| D DD DDD DDDD |2| d dd ddd dddd |3| YY YYYY a A |4| H HH h hh k kk i ii e |5| m mm s ss |6| Do DDDo Q Qo QQ |7| N NN |8| M/D/YYYY N-HH:mm:ss Qo?a')
+	assert res == '0 00 0th Jan January |1| 0 00 0 000 |2| -1 Mo Mon Monday |3|  0 am AM |4| 0 00 12 12 1 01 0 00 e |5| 0 00 0 00 |6| 0th 0th 1 1st 01 |7| AD Anno Domini |8| 0/0/0 AD-00:00:00 1st?am'
+}
diff --git a/vlib/time/format.v b/vlib/time/format.v
index 8922d615e8..ec45b087e1 100644
--- a/vlib/time/format.v
+++ b/vlib/time/format.v
@@ -5,6 +5,16 @@ module time
 
 import strings
 
+fn iclamp(x int, a int, b int) int {
+	if x < a {
+		return a
+	}
+	if x > b {
+		return b
+	}
+	return x
+}
+
 // int_to_byte_array_no_pad fulfill buffer by part
 // it doesn't pad with leading zeros for performance reasons
 @[direct_array_access]
@@ -401,20 +411,10 @@ pub fn (t Time) custom_format(s string) string {
 				sb.write_string(ordinal_suffix(t.month))
 			}
 			'MMM' {
-				m := if t.month >= 1 && t.month <= 12 {
-					long_months[t.month - 1][0..3]
-				} else {
-					long_months[0][0..3]
-				}
-				sb.write_string(m)
+				sb.write_string(long_months[iclamp(0, t.month - 1, 11)][0..3])
 			}
 			'MMMM' {
-				m := if t.month >= 1 && t.month <= 12 {
-					long_months[t.month - 1]
-				} else {
-					long_months[0]
-				}
-				sb.write_string(m)
+				sb.write_string(long_months[iclamp(0, t.month - 1, 11)])
 			}
 			'D' {
 				sb.write_string(t.day.str())
@@ -438,16 +438,16 @@ pub fn (t Time) custom_format(s string) string {
 				sb.write_string('${t.day_of_week() % 7}')
 			}
 			'dd' {
-				sb.write_string(long_days[t.day_of_week() - 1][0..2])
+				sb.write_string(long_days[iclamp(0, t.day_of_week() - 1, 6)][0..2])
 			}
 			'ddd' {
-				sb.write_string(long_days[t.day_of_week() - 1][0..3])
+				sb.write_string(long_days[iclamp(0, t.day_of_week() - 1, 6)][0..3])
 			}
 			'dddd' {
-				sb.write_string(long_days[t.day_of_week() - 1])
+				sb.write_string(long_days[iclamp(0, t.day_of_week() - 1, 6)])
 			}
 			'YY' {
-				sb.write_string(t.year.str()[2..4])
+				sb.write_string(t.year.str()#[2..4])
 			}
 			'YYYY' {
 				sb.write_string(t.year.str())
diff --git a/vlib/time/time.v b/vlib/time/time.v
index 8b82041264..9e18c8ef52 100644
--- a/vlib/time/time.v
+++ b/vlib/time/time.v
@@ -288,7 +288,7 @@ pub fn day_of_week(y int, m int, d int) int {
 	if m < 3 {
 		sy = sy - 1
 	}
-	return (sy + sy / 4 - sy / 100 + sy / 400 + t[m - 1] + d - 1) % 7 + 1
+	return (sy + sy / 4 - sy / 100 + sy / 400 + t[iclamp(0, m - 1, 11)] + d - 1) % 7 + 1
 }
 
 // day_of_week returns the current day as an integer.
@@ -330,7 +330,7 @@ pub fn (t Time) week_of_year() int {
 // year_day returns the current day of the year as an integer.
 // See also #Time.custom_format .
 pub fn (t Time) year_day() int {
-	yday := t.day + days_before[t.month - 1]
+	yday := t.day + days_before[iclamp(0, t.month - 1, 12)]
 	if is_leap_year(t.year) && t.month > 2 {
 		return yday + 1
 	}
@@ -340,13 +340,13 @@ pub fn (t Time) year_day() int {
 // weekday_str returns the current day as a string 3 letter abbreviation.
 pub fn (t Time) weekday_str() string {
 	i := t.day_of_week() - 1
-	return long_days[i][0..3]
+	return long_days[iclamp(0, i, 6)][0..3]
 }
 
 // long_weekday_str returns the current day as a string.
 pub fn (t Time) long_weekday_str() string {
 	i := t.day_of_week() - 1
-	return long_days[i]
+	return long_days[iclamp(0, i, 6)]
 }
 
 // is_leap_year checks if a given a year is a leap year.