diff --git a/lib/iso8601/unit.ex b/lib/iso8601/unit.ex
index 0bff437..33467fc 100644
--- a/lib/iso8601/unit.ex
+++ b/lib/iso8601/unit.ex
@@ -24,8 +24,8 @@ defmodule Tempo.Iso8601.Unit do
   }
 
   @unit_after %{
-    year: {:month, 1..-1},
-    month: {:day, 1..-1},
+    year: {:month, 1..-1//-1},
+    month: {:day, 1..-1//-1},
     week: {:day_of_week, 1..7},
     day: {:hour, 0..23},
     hour: {:minute, 0..59},
@@ -54,10 +54,10 @@ defmodule Tempo.Iso8601.Unit do
 
   """
   def implicit_enumerator(:year = unit, calendar) do
-    if calendar.calendar_base == :month do
+    if calendar.calendar_base() == :month do
       Map.get(@unit_after, unit)
     else
-      {:week, 1..-1}
+      {:week, 1..-1//-1}
     end
   end
 
diff --git a/lib/validation.ex b/lib/validation.ex
index 439e3a9..42f0ec8 100644
--- a/lib/validation.ex
+++ b/lib/validation.ex
@@ -132,7 +132,7 @@ defmodule Tempo.Validation do
 
     with {:ok, week} <- conform(week, 1..weeks_in_year),
          [day_of_week: day] <- resolve([day_of_week: day], calendar) do
-      year_week_day(year, week, day, rest, calendar.calendar_base, calendar)
+      year_week_day(year, week, day, rest, calendar.calendar_base(), calendar)
     end
   end