diff --git a/fixedcal/core/date.py b/fixedcal/core/date.py
index beea0fd..70f86cc 100644
--- a/fixedcal/core/date.py
+++ b/fixedcal/core/date.py
@@ -43,7 +43,7 @@ class FixedDate:
             tuple: day of year (1...366) and year (1...9999) in a tuple
         """
         day_of_year = date.timetuple().tm_yday
-        return self._from_day_of_year(day_of_year, date.year)
+        return (day_of_year, date.year)
 
     def _from_fixed_date(self, day: int, month: int, year: int) -> tuple:
         is_this_leap_year = is_leap_year(year)
@@ -69,6 +69,10 @@ class FixedDate:
         Returns:
             tuple: day of year (1...366) and year (1...9999) in a tuple
         """
+        max_day_of_year = 366 if is_leap_year(year) else 365
+        if day_of_year < 1 or day_of_year > max_day_of_year:
+            raise ValueError("Invalid day of year")
+
         return (day_of_year, year)
 
     @classmethod
diff --git a/tests/basic_day_of_year_test.py b/tests/basic_day_of_year_test.py
index d5eb740..c6abb6d 100644
--- a/tests/basic_day_of_year_test.py
+++ b/tests/basic_day_of_year_test.py
@@ -35,6 +35,20 @@ class TestBasicDayOfYearInit(unittest.TestCase):
         self.assertEqual(fixed_date.day_of_month, 29)
         self.assertTrue(fixed_date.is_year_day)
 
+    def test_day_of_year_zero(self):
+        self.assertRaises(ValueError, lambda : FixedDate(day_of_year=0, year=2022))
+
+    def test_day_of_year_negative(self):
+        self.assertRaises(ValueError, lambda : FixedDate(day_of_year=-1, year=2022))
+
+    def test_day_of_year_above_maximum_non_leap_year(self):
+        # 2022 is not a leap year, so there is no 366th day of year
+        self.assertRaises(ValueError, lambda : FixedDate(day_of_year=366, year=2022))
+
+    def test_day_of_year_above_maximum_leap_year(self):
+        # 2024 is a leap year, but there is no 367th day of year
+        self.assertRaises(ValueError, lambda : FixedDate(day_of_year=367, year=2024))
+
     def test_init_day_of_year_with_none_arguments(self):
         fixed_date = FixedDate(None, 1, None, None, 2022)
         self.assertEqual(fixed_date.date, datetime.date(2022, 1, 1))