diff --git a/test/data/integer/valid_integer_data.gleam b/test/data/integer/valid_integer_data.gleam
index 65f00d8..0ead67e 100644
--- a/test/data/integer/valid_integer_data.gleam
+++ b/test/data/integer/valid_integer_data.gleam
@@ -586,6 +586,17 @@ fn valid_whitespace() -> List(IntegerTestData) {
   ]
 }
 
+fn valid_mixed() -> List(IntegerTestData) {
+  [
+    IntegerTestData(
+      input: "  \n+1990_04_12",
+      base: base_0,
+      expected_program_output: Ok(19_900_412),
+      expected_python_output: Ok("19900412"),
+    ),
+  ]
+}
+
 pub fn data() -> List(IntegerTestData) {
   [
     valid_simple(),
@@ -595,6 +606,7 @@ pub fn data() -> List(IntegerTestData) {
     valid_underscore(),
     valid_whitespace(),
     valid_simple_base_prefix(),
+    valid_mixed(),
   ]
   |> list.flatten
 }
diff --git a/test/tokenizer_test.gleam b/test/tokenizer_test.gleam
index 1be4c4d..5a6f69b 100644
--- a/test/tokenizer_test.gleam
+++ b/test/tokenizer_test.gleam
@@ -11,8 +11,8 @@ import lenient_parse/internal/token.{
 import lenient_parse/internal/tokenizer
 import startest/expect
 
-// In Python's `float()`, only base 10 is supported. Any letter character
-// (a-z/A-Z), outside of an exponent character, should be considered an Unknown.
+// With floats, only base 10 is supported. Any letter character (a-z/A-Z),
+// outside of an exponent character, should be considered an Unknown.
 pub fn tokenize_float_test() {
   " \t\n\r\f\r\n+-0123456789eE._abc"
   |> tokenizer.tokenize_float
@@ -45,10 +45,10 @@ pub fn tokenize_float_test() {
   ])
 }
 
-// In Python's `int()`, Letter characters (a-z/A-Z) are all supported given the
-// right base, so we mark these as Digits.
-pub fn tokenize_int_base_10_test() {
-  " \t\n\r\f\r\n+-0123456789eE._abcZ"
+// With integers, Letter characters (a-z/A-Z) are all supported given the right
+// base, so we mark these as Digits.
+pub fn tokenize_int_test() {
+  " \t\n\r\f\r\n+-abcdefghijklmnopqrstuvwxyz._ABCDEFGHIJKLMNOPQRSTUVWXYZ"
   |> tokenizer.tokenize_int
   |> expect.to_equal([
     Whitespace(#(0, 1), space),
@@ -59,368 +59,63 @@ pub fn tokenize_int_base_10_test() {
     Whitespace(#(5, 6), windows_newline),
     Sign(#(6, 7), "+", True),
     Sign(#(7, 8), "-", False),
-    Digit(#(8, 9), "0", 0),
-    Digit(#(9, 10), "1", 1),
-    Digit(#(10, 11), "2", 2),
-    Digit(#(11, 12), "3", 3),
-    Digit(#(12, 13), "4", 4),
-    Digit(#(13, 14), "5", 5),
-    Digit(#(14, 15), "6", 6),
-    Digit(#(15, 16), "7", 7),
-    Digit(#(16, 17), "8", 8),
-    Digit(#(17, 18), "9", 9),
-    Digit(#(18, 19), "e", 14),
-    Digit(#(19, 20), "E", 14),
-    Unknown(#(20, 21), "."),
-    Underscore(#(21, 22)),
-    Digit(#(22, 23), "a", 10),
-    Digit(#(23, 24), "b", 11),
-    Digit(#(24, 25), "c", 12),
-    Digit(#(25, 26), "Z", 35),
-  ])
-}
-
-pub fn tokenize_int_base_2_test() {
-  "0102101"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "1", 1),
-    Digit(#(2, 3), "0", 0),
-    Digit(#(3, 4), "2", 2),
-    Digit(#(4, 5), "1", 1),
-    Digit(#(5, 6), "0", 0),
-    Digit(#(6, 7), "1", 1),
-  ])
-}
-
-pub fn tokenize_int_base_16_test() {
-  "dead_beefZ"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "d", 0xD),
-    Digit(#(1, 2), "e", 0xE),
-    Digit(#(2, 3), "a", 0xA),
-    Digit(#(3, 4), "d", 0xD),
-    Underscore(#(4, 5)),
-    Digit(#(5, 6), "b", 0xB),
-    Digit(#(6, 7), "e", 0xE),
-    Digit(#(7, 8), "e", 0xE),
-    Digit(#(8, 9), "f", 0xF),
-    Digit(#(9, 10), "Z", 35),
-  ])
-}
-
-pub fn tokenize_int_base_35_test() {
-  "1234567890abcdefghijklmnopqrstuvwxyz"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "1", 1),
-    Digit(#(1, 2), "2", 2),
-    Digit(#(2, 3), "3", 3),
-    Digit(#(3, 4), "4", 4),
-    Digit(#(4, 5), "5", 5),
-    Digit(#(5, 6), "6", 6),
-    Digit(#(6, 7), "7", 7),
-    Digit(#(7, 8), "8", 8),
-    Digit(#(8, 9), "9", 9),
-    Digit(#(9, 10), "0", 0),
-    Digit(#(10, 11), "a", 10),
-    Digit(#(11, 12), "b", 11),
-    Digit(#(12, 13), "c", 12),
-    Digit(#(13, 14), "d", 13),
-    Digit(#(14, 15), "e", 14),
-    Digit(#(15, 16), "f", 15),
-    Digit(#(16, 17), "g", 16),
-    Digit(#(17, 18), "h", 17),
-    Digit(#(18, 19), "i", 18),
-    Digit(#(19, 20), "j", 19),
-    Digit(#(20, 21), "k", 20),
-    Digit(#(21, 22), "l", 21),
-    Digit(#(22, 23), "m", 22),
-    Digit(#(23, 24), "n", 23),
-    Digit(#(24, 25), "o", 24),
-    Digit(#(25, 26), "p", 25),
-    Digit(#(26, 27), "q", 26),
-    Digit(#(27, 28), "r", 27),
-    Digit(#(28, 29), "s", 28),
-    Digit(#(29, 30), "t", 29),
-    Digit(#(30, 31), "u", 30),
-    Digit(#(31, 32), "v", 31),
-    Digit(#(32, 33), "w", 32),
-    Digit(#(33, 34), "x", 33),
-    Digit(#(34, 35), "y", 34),
-    Digit(#(35, 36), "z", 35),
-  ])
-}
-
-pub fn tokenize_int_base_36_test() {
-  "159az"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "1", 1),
-    Digit(#(1, 2), "5", 5),
-    Digit(#(2, 3), "9", 9),
-    Digit(#(3, 4), "a", 10),
-    Digit(#(4, 5), "z", 35),
-  ])
-}
-
-pub fn tokenize_int_with_0b_prefix_and_base_0_test() {
-  "   0b1010b"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Whitespace(#(0, 1), space),
-    Whitespace(#(1, 2), space),
-    Whitespace(#(2, 3), space),
-    Digit(#(3, 4), "0", 0),
-    Digit(#(4, 5), "b", 11),
-    Digit(#(5, 6), "1", 1),
-    Digit(#(6, 7), "0", 0),
-    Digit(#(7, 8), "1", 1),
-    Digit(#(8, 9), "0", 0),
-    Digit(#(9, 10), "b", 11),
-  ])
-}
-
-pub fn tokenize_int_with_0o_prefix_and_base_0_test() {
-  "   0o0123456780o"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Whitespace(#(0, 1), space),
-    Whitespace(#(1, 2), space),
-    Whitespace(#(2, 3), space),
-    Digit(#(3, 4), "0", 0),
-    Digit(#(4, 5), "o", 24),
-    Digit(#(5, 6), "0", 0),
-    Digit(#(6, 7), "1", 1),
-    Digit(#(7, 8), "2", 2),
-    Digit(#(8, 9), "3", 3),
-    Digit(#(9, 10), "4", 4),
-    Digit(#(10, 11), "5", 5),
-    Digit(#(11, 12), "6", 6),
-    Digit(#(12, 13), "7", 7),
-    Digit(#(13, 14), "8", 8),
-    Digit(#(14, 15), "0", 0),
-    Digit(#(15, 16), "o", 24),
-  ])
-}
-
-pub fn tokenize_int_with_0x_prefix_and_base_0_test() {
-  " +0XDEAD_BEEF0x "
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Whitespace(#(0, 1), space),
-    Sign(#(1, 2), "+", True),
-    Digit(#(2, 3), "0", 0),
-    Digit(#(3, 4), "X", 33),
-    Digit(#(4, 5), "D", 13),
-    Digit(#(5, 6), "E", 14),
-    Digit(#(6, 7), "A", 10),
-    Digit(#(7, 8), "D", 13),
-    Underscore(#(8, 9)),
-    Digit(#(9, 10), "B", 11),
-    Digit(#(10, 11), "E", 14),
-    Digit(#(11, 12), "E", 14),
-    Digit(#(12, 13), "F", 15),
-    Digit(#(13, 14), "0", 0),
-    Digit(#(14, 15), "x", 33),
-    Whitespace(#(15, 16), space),
-  ])
-}
-
-pub fn tokenize_int_with_0b_prefix_and_base_2_test() {
-  "   0b1010 a"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Whitespace(#(0, 1), space),
-    Whitespace(#(1, 2), space),
-    Whitespace(#(2, 3), space),
-    Digit(#(3, 4), "0", 0),
-    Digit(#(4, 5), "b", 11),
-    Digit(#(5, 6), "1", 1),
-    Digit(#(6, 7), "0", 0),
-    Digit(#(7, 8), "1", 1),
-    Digit(#(8, 9), "0", 0),
-    Whitespace(#(9, 10), space),
-    Digit(#(10, 11), "a", 10),
-  ])
-}
-
-pub fn tokenize_int_with_0o_prefix_and_base_8_test() {
-  "   0o77 a"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Whitespace(#(0, 1), space),
-    Whitespace(#(1, 2), space),
-    Whitespace(#(2, 3), space),
-    Digit(#(3, 4), "0", 0),
-    Digit(#(4, 5), "o", 24),
-    Digit(#(5, 6), "7", 7),
-    Digit(#(6, 7), "7", 7),
-    Whitespace(#(7, 8), space),
     Digit(#(8, 9), "a", 10),
+    Digit(#(9, 10), "b", 11),
+    Digit(#(10, 11), "c", 12),
+    Digit(#(11, 12), "d", 13),
+    Digit(#(12, 13), "e", 14),
+    Digit(#(13, 14), "f", 15),
+    Digit(#(14, 15), "g", 16),
+    Digit(#(15, 16), "h", 17),
+    Digit(#(16, 17), "i", 18),
+    Digit(#(17, 18), "j", 19),
+    Digit(#(18, 19), "k", 20),
+    Digit(#(19, 20), "l", 21),
+    Digit(#(20, 21), "m", 22),
+    Digit(#(21, 22), "n", 23),
+    Digit(#(22, 23), "o", 24),
+    Digit(#(23, 24), "p", 25),
+    Digit(#(24, 25), "q", 26),
+    Digit(#(25, 26), "r", 27),
+    Digit(#(26, 27), "s", 28),
+    Digit(#(27, 28), "t", 29),
+    Digit(#(28, 29), "u", 30),
+    Digit(#(29, 30), "v", 31),
+    Digit(#(30, 31), "w", 32),
+    Digit(#(31, 32), "x", 33),
+    Digit(#(32, 33), "y", 34),
+    Digit(#(33, 34), "z", 35),
+    Unknown(#(34, 35), "."),
+    Underscore(#(35, 36)),
+    Digit(#(36, 37), "A", 10),
+    Digit(#(37, 38), "B", 11),
+    Digit(#(38, 39), "C", 12),
+    Digit(#(39, 40), "D", 13),
+    Digit(#(40, 41), "E", 14),
+    Digit(#(41, 42), "F", 15),
+    Digit(#(42, 43), "G", 16),
+    Digit(#(43, 44), "H", 17),
+    Digit(#(44, 45), "I", 18),
+    Digit(#(45, 46), "J", 19),
+    Digit(#(46, 47), "K", 20),
+    Digit(#(47, 48), "L", 21),
+    Digit(#(48, 49), "M", 22),
+    Digit(#(49, 50), "N", 23),
+    Digit(#(50, 51), "O", 24),
+    Digit(#(51, 52), "P", 25),
+    Digit(#(52, 53), "Q", 26),
+    Digit(#(53, 54), "R", 27),
+    Digit(#(54, 55), "S", 28),
+    Digit(#(55, 56), "T", 29),
+    Digit(#(56, 57), "U", 30),
+    Digit(#(57, 58), "V", 31),
+    Digit(#(58, 59), "W", 32),
+    Digit(#(59, 60), "X", 33),
+    Digit(#(60, 61), "Y", 34),
+    Digit(#(61, 62), "Z", 35),
   ])
 }
 
-pub fn tokenize_int_with_0x_prefix_and_base_16_test() {
-  "   0x_ABC ."
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Whitespace(#(0, 1), space),
-    Whitespace(#(1, 2), space),
-    Whitespace(#(2, 3), space),
-    Digit(#(3, 4), "0", 0),
-    Digit(#(4, 5), "x", 33),
-    Underscore(#(5, 6)),
-    Digit(#(6, 7), "A", 10),
-    Digit(#(7, 8), "B", 11),
-    Digit(#(8, 9), "C", 12),
-    Whitespace(#(9, 10), space),
-    Unknown(#(10, 11), "."),
-  ])
-}
-
-// ---- Uppercase / lowercase prefix with base 0 tests
-
-pub fn tokenize_int_with_lowercase_binary_prefix_and_base_0_test() {
-  "0b101"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "b", 11),
-    Digit(#(2, 3), "1", 1),
-    Digit(#(3, 4), "0", 0),
-    Digit(#(4, 5), "1", 1),
-  ])
-}
-
-pub fn tokenize_int_with_uppercase_binary_prefix_and_base_0_test() {
-  "0B101"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "B", 11),
-    Digit(#(2, 3), "1", 1),
-    Digit(#(3, 4), "0", 0),
-    Digit(#(4, 5), "1", 1),
-  ])
-}
-
-pub fn tokenize_int_with_lowercase_octal_prefix_and_base_0_test() {
-  "0o777"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "o", 24),
-    Digit(#(2, 3), "7", 7),
-    Digit(#(3, 4), "7", 7),
-    Digit(#(4, 5), "7", 7),
-  ])
-}
-
-pub fn tokenize_int_with_uppercase_octal_prefix_and_base_0_test() {
-  "0O777"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "O", 24),
-    Digit(#(2, 3), "7", 7),
-    Digit(#(3, 4), "7", 7),
-    Digit(#(4, 5), "7", 7),
-  ])
-}
-
-pub fn tokenize_int_with_lowercase_hexadecimal_prefix_and_base_0_test() {
-  "0xABC"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "x", 33),
-    Digit(#(2, 3), "A", 10),
-    Digit(#(3, 4), "B", 11),
-    Digit(#(4, 5), "C", 12),
-  ])
-}
-
-pub fn tokenize_int_with_uppercase_hexadecimal_prefix_and_base_0_test() {
-  "0XABC"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "X", 33),
-    Digit(#(2, 3), "A", 10),
-    Digit(#(3, 4), "B", 11),
-    Digit(#(4, 5), "C", 12),
-  ])
-}
-
-pub fn tokenize_int_with_no_prefix_and_base_0_test() {
-  "  \n+1990_04_12.0e4 "
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Whitespace(#(0, 1), space),
-    Whitespace(#(1, 2), space),
-    Whitespace(#(2, 3), line_feed),
-    Sign(#(3, 4), "+", True),
-    Digit(#(4, 5), "1", 1),
-    Digit(#(5, 6), "9", 9),
-    Digit(#(6, 7), "9", 9),
-    Digit(#(7, 8), "0", 0),
-    Underscore(#(8, 9)),
-    Digit(#(9, 10), "0", 0),
-    Digit(#(10, 11), "4", 4),
-    Underscore(#(11, 12)),
-    Digit(#(12, 13), "1", 1),
-    Digit(#(13, 14), "2", 2),
-    Unknown(#(14, 15), "."),
-    Digit(#(15, 16), "0", 0),
-    Digit(#(16, 17), "e", 14),
-    Digit(#(17, 18), "4", 4),
-    Whitespace(#(18, 19), space),
-  ])
-}
-
-// ---- Tests for matching base prefixes and specified bases
-
-pub fn tokenize_int_with_base_2_and_binary_prefix_test() {
-  "0b101"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "b", 11),
-    Digit(#(2, 3), "1", 1),
-    Digit(#(3, 4), "0", 0),
-    Digit(#(4, 5), "1", 1),
-  ])
-}
-
-pub fn tokenize_int_with_base_8_and_octal_prefix_test() {
-  "0o777"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "o", 24),
-    Digit(#(2, 3), "7", 7),
-    Digit(#(3, 4), "7", 7),
-    Digit(#(4, 5), "7", 7),
-  ])
-}
-
-pub fn tokenize_int_with_base_16_and_hexadecimal_prefix_test() {
-  "0xABC"
-  |> tokenizer.tokenize_int
-  |> expect.to_equal([
-    Digit(#(0, 1), "0", 0),
-    Digit(#(1, 2), "x", 33),
-    Digit(#(2, 3), "A", 10),
-    Digit(#(3, 4), "B", 11),
-    Digit(#(4, 5), "C", 12),
-  ])
-}
-
-// ---- Tests for all whitespace characters
-
 pub fn tokenize_int_with_all_whitespace_characters_test() {
   let whitespace_character_strings = whitespace.character_dict() |> dict.to_list