diff --git a/lib/elixir/lib/calendar/iso.ex b/lib/elixir/lib/calendar/iso.ex
index 5740cc31272..183a1573200 100644
--- a/lib/elixir/lib/calendar/iso.ex
+++ b/lib/elixir/lib/calendar/iso.ex
@@ -1,3 +1,11 @@
+defmodule Ascii do
+  defmacro int(x) do
+    quote do
+      <<3::4, unquote(x)::4>>
+    end
+  end
+end
+
 defmodule Calendar.ISO do
   @moduledoc """
   The default calendar implementation, a Gregorian calendar following ISO 8601.
@@ -200,18 +208,20 @@ defmodule Calendar.ISO do
   # on ~D[0001-01-01] which is 366 days later.
   @iso_epoch 366
 
+  import Ascii
+
   [match_basic_date, match_ext_date, guard_date, read_date] =
     quote do
       [
-        <<y1, y2, y3, y4, m1, m2, d1, d2>>,
-        <<y1, y2, y3, y4, @ext_date_sep, m1, m2, @ext_date_sep, d1, d2>>,
-        y1 >= ?0 and y1 <= ?9 and y2 >= ?0 and y2 <= ?9 and y3 >= ?0 and y3 <= ?9 and y4 >= ?0 and
-          y4 <= ?9 and m1 >= ?0 and m1 <= ?9 and m2 >= ?0 and m2 <= ?9 and d1 >= ?0 and d1 <= ?9 and
-          d2 >= ?0 and d2 <= ?9,
+        <<int(y1), int(y2), int(y3), int(y4), int(m1), int(m2), int(d1), int(d2)>>,
+        <<int(y1), int(y2), int(y3), int(y4), @ext_date_sep, int(m1), int(m2), @ext_date_sep,
+          int(d1), int(d2)>>,
+        y1 <= 9 and y2 <= 9 and y3 <= 9 and y4 <= 9 and m1 <= 9 and m2 <= 9 and d1 <= 9 and
+          d2 <= 9,
         {
-          (y1 - ?0) * 1000 + (y2 - ?0) * 100 + (y3 - ?0) * 10 + (y4 - ?0),
-          (m1 - ?0) * 10 + (m2 - ?0),
-          (d1 - ?0) * 10 + (d2 - ?0)
+          y1 * 1000 + y2 * 100 + y3 * 10 + y4,
+          m1 * 10 + m2,
+          d1 * 10 + d2
         }
       ]
     end
@@ -219,14 +229,13 @@ defmodule Calendar.ISO do
   [match_basic_time, match_ext_time, guard_time, read_time] =
     quote do
       [
-        <<h1, h2, i1, i2, s1, s2>>,
-        <<h1, h2, @ext_time_sep, i1, i2, @ext_time_sep, s1, s2>>,
-        h1 >= ?0 and h1 <= ?9 and h2 >= ?0 and h2 <= ?9 and i1 >= ?0 and i1 <= ?9 and i2 >= ?0 and
-          i2 <= ?9 and s1 >= ?0 and s1 <= ?9 and s2 >= ?0 and s2 <= ?9,
+        <<int(h1), int(h2), int(i1), int(i2), int(s1), int(s2)>>,
+        <<int(h1), int(h2), @ext_time_sep, int(i1), int(i2), @ext_time_sep, int(s1), int(s2)>>,
+        h1 <= 9 and h2 <= 9 and i1 <= 9 and i2 <= 9 and s1 <= 9 and s2 <= 9,
         {
-          (h1 - ?0) * 10 + (h2 - ?0),
-          (i1 - ?0) * 10 + (i2 - ?0),
-          (s1 - ?0) * 10 + (s2 - ?0)
+          h1 * 10 + h2,
+          i1 * 10 + i2,
+          s1 * 10 + s2
         }
       ]
     end
@@ -2021,34 +2030,38 @@ defmodule Calendar.ISO do
   defp parse_offset("Z"), do: {0, ""}
   defp parse_offset("-00:00"), do: :error
 
-  defp parse_offset(<<?+, h1, h2, ?:, m1, m2, rest::binary>>),
+  defp parse_offset(<<?+, int(h1), int(h2), ?:, int(m1), int(m2), rest::binary>>),
     do: parse_offset(1, h1, h2, m1, m2, rest)
 
-  defp parse_offset(<<?-, h1, h2, ?:, m1, m2, rest::binary>>),
+  defp parse_offset(<<?-, int(h1), int(h2), ?:, int(m1), int(m2), rest::binary>>),
     do: parse_offset(-1, h1, h2, m1, m2, rest)
 
-  defp parse_offset(<<?+, h1, h2, m1, m2, rest::binary>>),
+  defp parse_offset(<<?+, int(h1), int(h2), int(m1), int(m2), rest::binary>>),
     do: parse_offset(1, h1, h2, m1, m2, rest)
 
-  defp parse_offset(<<?-, h1, h2, m1, m2, rest::binary>>),
+  defp parse_offset(<<?-, int(h1), int(h2), int(m1), int(m2), rest::binary>>),
     do: parse_offset(-1, h1, h2, m1, m2, rest)
 
-  defp parse_offset(<<?+, h1, h2, rest::binary>>), do: parse_offset(1, h1, h2, ?0, ?0, rest)
-  defp parse_offset(<<?-, h1, h2, rest::binary>>), do: parse_offset(-1, h1, h2, ?0, ?0, rest)
+  defp parse_offset(<<?+, int(h1), int(h2), rest::binary>>),
+    do: parse_offset(1, h1, h2, 0, 0, rest)
+
+  defp parse_offset(<<?-, int(h1), int(h2), rest::binary>>),
+    do: parse_offset(-1, h1, h2, 0, 0, rest)
+
   defp parse_offset(_), do: :error
 
-  defp parse_offset(sign, h1, h2, m1, m2, rest) do
-    with true <- h1 in ?0..?2 and h2 in ?0..?9,
-         true <- m1 in ?0..?5 and m2 in ?0..?9,
-         hour = (h1 - ?0) * 10 + h2 - ?0,
-         min = (m1 - ?0) * 10 + m2 - ?0,
-         true <- hour < 24 do
+  defp parse_offset(sign, h1, h2, m1, m2, rest)
+       when h2 < 10 and m1 < 6 and m2 < 10 do
+    with hour when hour < 24 <- h1 * 10 + h2,
+         min = m1 * 10 + m2 do
       {(hour * 60 + min) * 60 * sign, rest}
     else
       _ -> :error
     end
   end
 
+  defp parse_offset(_, _, _, _, _, _), do: :error
+
   @doc false
   def gregorian_seconds_to_iso_days(seconds, microsecond) do
     {days, rest_seconds} = div_rem(seconds, @seconds_per_day)