diff --git a/src/request/mod.rs b/src/request/mod.rs
index db27c6e..2c83f14 100644
--- a/src/request/mod.rs
+++ b/src/request/mod.rs
@@ -135,23 +135,3 @@ define_tokens_128! {
     XOAUTH,
     XOAUTH2,
 }
-
-/*
- * Adapted from Daniel Lemire's source:
- * https://github.com/lemire/Code-used-on-Daniel-Lemire-s-blog/blob/master/2019/04/17/hexparse.cpp
- *
- */
-
-pub(crate) static HEX_MAP: &[i8] = &[
-    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1, -1, 10, 11, 12, 13, 14, 15, -1, -1, -1,
-    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 10,
-    11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-];
diff --git a/src/request/parser.rs b/src/request/parser.rs
index f4f5f0a..e05d406 100644
--- a/src/request/parser.rs
+++ b/src/request/parser.rs
@@ -583,19 +583,15 @@ impl<'x, 'y> Rfc5321Parser<'x, 'y> {
                     return Ok(value.into_string());
                 }
                 b'+' => {
-                    let mut hex1 = 0;
+                    let mut hex1 = None;
 
                     while let Some(&ch) = self.bytes.next() {
-                        if ch.is_ascii_hexdigit() {
-                            if hex1 != 0 {
-                                let hex1 = HEX_MAP[hex1 as usize];
-                                let hex2 = HEX_MAP[ch as usize];
-                                if hex1 != -1 && hex2 != -1 {
-                                    value.push(((hex1 as u8) << 4) | hex2 as u8);
-                                }
+                        if let Some(digit) = char::from(ch).to_digit(16) {
+                            if let Some(hex1) = hex1 {
+                                value.push(((hex1 as u8) << 4) | digit as u8);
                                 break;
                             } else {
-                                hex1 = ch;
+                                hex1 = Some(digit);
                             }
                         } else if ch == LF {
                             self.stop_char = b'\n';