diff --git a/src/token.rs b/src/token.rs
index 36e51903..72e733d3 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -922,6 +922,32 @@ pub fn get_next_token(
     result
 }
 
+/// Test if the given character is a hex character.
+fn is_hex_char(c: char) -> bool {
+    match c {
+        'a'..='f' => true,
+        'A'..='F' => true,
+        '0'..='9' => true,
+        _ => false,
+    }
+}
+
+/// Test if the given character is an octal character.
+fn is_octal_char(c: char) -> bool {
+    match c {
+        '0'..='7' => true,
+        _ => false,
+    }
+}
+
+/// Test if the given character is a binary character.
+fn is_binary_char(c: char) -> bool {
+    match c {
+        '0' | '1' => true,
+        _ => false,
+    }
+}
+
 /// Get the next token.
 fn get_next_token_inner(
     stream: &mut impl InputStream,
@@ -984,18 +1010,9 @@ fn get_next_token_inner(
                             eat_next(stream, pos);
 
                             let valid = match ch {
-                                'x' | 'X' => [
-                                    'a', 'b', 'c', 'd', 'e', 'f', 'A', 'B', 'C', 'D', 'E', 'F',
-                                    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '_',
-                                ],
-                                'o' | 'O' => [
-                                    '0', '1', '2', '3', '4', '5', '6', '7', '_', '_', '_', '_',
-                                    '_', '_', '_', '_', '_', '_', '_', '_', '_', '_', '_',
-                                ],
-                                'b' | 'B' => [
-                                    '0', '1', '_', '_', '_', '_', '_', '_', '_', '_', '_', '_',
-                                    '_', '_', '_', '_', '_', '_', '_', '_', '_', '_', '_',
-                                ],
+                                'x' | 'X' => is_hex_char,
+                                'o' | 'O' => is_octal_char,
+                                'b' | 'B' => is_binary_char,
                                 _ => unreachable!(),
                             };
 
@@ -1007,7 +1024,7 @@ fn get_next_token_inner(
                             });
 
                             while let Some(next_char_in_escape_seq) = stream.peek_next() {
-                                if !valid.contains(&next_char_in_escape_seq) {
+                                if !valid(next_char_in_escape_seq) {
                                     break;
                                 }
 
diff --git a/tests/number_literals.rs b/tests/number_literals.rs
index 699de19a..ce19b52d 100644
--- a/tests/number_literals.rs
+++ b/tests/number_literals.rs
@@ -14,6 +14,7 @@ fn test_hex_literal() -> Result<(), Box<EvalAltResult>> {
     let engine = Engine::new();
 
     assert_eq!(engine.eval::<INT>("let x = 0xf; x")?, 15);
+    assert_eq!(engine.eval::<INT>("let x = 0Xf; x")?, 15);
     assert_eq!(engine.eval::<INT>("let x = 0xff; x")?, 255);
 
     Ok(())
@@ -24,6 +25,7 @@ fn test_octal_literal() -> Result<(), Box<EvalAltResult>> {
     let engine = Engine::new();
 
     assert_eq!(engine.eval::<INT>("let x = 0o77; x")?, 63);
+    assert_eq!(engine.eval::<INT>("let x = 0O77; x")?, 63);
     assert_eq!(engine.eval::<INT>("let x = 0o1234; x")?, 668);
 
     Ok(())
@@ -34,6 +36,7 @@ fn test_binary_literal() -> Result<(), Box<EvalAltResult>> {
     let engine = Engine::new();
 
     assert_eq!(engine.eval::<INT>("let x = 0b1111; x")?, 15);
+    assert_eq!(engine.eval::<INT>("let x = 0B1111; x")?, 15);
     assert_eq!(
         engine.eval::<INT>("let x = 0b0011_1100_1010_0101; x")?,
         15525