diff --git a/2023/Cargo.toml b/2023/Cargo.toml
index d855299..7000a92 100644
--- a/2023/Cargo.toml
+++ b/2023/Cargo.toml
@@ -6,10 +6,10 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+aho-corasick = "1.1.2"
 anyhow = "1.0.75"
 clap = { version = "4.4.8", features = ["derive"] }
 nom = "7.1.3"
-regex = "1.10.2"
 
 [dev-dependencies]
 criterion = "0.5.1"
diff --git a/2023/src/day01.rs b/2023/src/day01.rs
index e96597e..d6025f8 100644
--- a/2023/src/day01.rs
+++ b/2023/src/day01.rs
@@ -1,5 +1,5 @@
+use aho_corasick::AhoCorasick;
 use anyhow::Result;
-use regex::bytes::Regex;
 
 pub fn part1(input: &[u8]) -> Result<String> {
     let mut it = input.iter();
@@ -22,43 +22,35 @@ pub fn part1(input: &[u8]) -> Result<String> {
     Ok(sum.to_string())
 }
 
-fn parse_string_digit(digit: &[u8]) -> Result<u32> {
-    Ok(match digit {
-        b"one" => 1,
-        b"two" => 2,
-        b"three" => 3,
-        b"four" => 4,
-        b"five" => 5,
-        b"six" => 6,
-        b"seven" => 7,
-        b"eight" => 8,
-        b"nine" => 9,
-        &[d] => u32::from(d - b'0'),
-        other => anyhow::bail!("invalid digit: {}", String::from_utf8_lossy(other)),
-    })
-}
-
-// 53255: too low
 pub fn part2(input: &[u8]) -> Result<String> {
-    let parser = Regex::new(r"[1-9]|one|two|three|four|five|six|seven|eight|nine")?;
+    let parser = AhoCorasick::new([
+        "1", "2", "3", "4", "5", "6", "7", "8", "9", "one", "two", "three", "four", "five", "six",
+        "seven", "eight", "nine",
+    ])?;
+
+    fn convert_id(id: u32) -> Result<u32> {
+        Ok(match id {
+            0..=8 => id + 1,
+            9..=17 => id - 8,
+            _ => anyhow::bail!("unreachable"),
+        })
+    }
+
     let mut sum = 0;
 
     for line in input.split(|&c| c == b'\n') {
         let mut first = None;
-        let mut last = &b""[..];
-
-        let mut start = 0;
+        let mut last = 0;
 
         // Cannot use find_iter because it doesn't find overlapping matches.
-        while let Some(needle) = parser.find_at(line, start) {
-            start = needle.start() + 1;
-            let digit = needle.as_bytes();
+        for needle in parser.find_overlapping_iter(line) {
+            let digit = convert_id(needle.pattern().as_u32())?;
             first.get_or_insert(digit);
             last = digit;
         }
 
         if let Some(first) = first {
-            sum += 10 * parse_string_digit(first)? + parse_string_digit(last)?;
+            sum += 10 * first + last;
         }
     }