diff --git a/2021/src/bin/day04.rs b/2021/src/bin/day04.rs
index cb445a0..32cbdac 100644
--- a/2021/src/bin/day04.rs
+++ b/2021/src/bin/day04.rs
@@ -57,10 +57,10 @@ fn has_won(board: &Board) -> bool {
 
 fn parse_input(raw: &str) -> BingoGame {
     let (input_numbers, boards) = raw.split_once("\n\n").unwrap();
-    let input_numbers = input_numbers.split(',').map(|n| n.parse().unwrap()).collect();
+    let input_numbers = input_numbers.split(',').map(parse_num).collect();
     let boards = boards
         .split("\n\n")
-        .map(|b| b.split_ascii_whitespace().map(|n| n.parse().unwrap()).collect())
+        .map(|b| b.split_ascii_whitespace().map(parse_num).collect())
         .map(|v: Vec<u8>| {
             debug_assert_eq!(v.len(), BOARD_SIZE * BOARD_SIZE);
             WINNING_INDICES.map(|row_or_col| row_or_col.map(|i| v[i]).to_vec()).to_vec()
diff --git a/2021/src/bin/day05.rs b/2021/src/bin/day05.rs
index df55afe..a1fd10a 100644
--- a/2021/src/bin/day05.rs
+++ b/2021/src/bin/day05.rs
@@ -20,7 +20,7 @@ fn parse_input(raw: &str) -> Parsed {
     raw.lines()
         .filter_map(|line| line.split_once(" -> "))
         .filter_map(|(c1, c2)| c1.split_once(',').zip(c2.split_once(',')))
-        .map(|((x1, y1), (x2, y2))| ((x1.parse().unwrap(), y1.parse().unwrap()), (x2.parse().unwrap(), y2.parse().unwrap())))
+        .map(|((x1, y1), (x2, y2))| ((parse_num(x1), parse_num(y1)), (parse_num(x2), parse_num(y2))))
         .collect()
 }
 
diff --git a/2021/src/common.rs b/2021/src/common.rs
index 7016ec3..71c26d6 100644
--- a/2021/src/common.rs
+++ b/2021/src/common.rs
@@ -1,5 +1,14 @@
 use std::env;
 
+#[cfg(not(debug_assertions))]
+use std::ops::{AddAssign, MulAssign};
+
+#[cfg(debug_assertions)]
+use std::{
+    fmt::{Debug, Display},
+    str::FromStr,
+};
+
 pub fn read_file(day: usize) -> String {
     std::fs::read_to_string(env::var("AOC_INPUT").unwrap_or_else(|_| format!("inputs/day{:0>2}", day))).unwrap()
 }
@@ -12,7 +21,18 @@ pub fn parse_nums_comma(l: &str) -> Vec<usize> {
     l.trim().split(',').map(parse_num).collect()
 }
 
-#[inline]
-fn parse_num(s: &str) -> usize {
+#[cfg(debug_assertions)]
+pub fn parse_num<T: FromStr<Err: Debug> + Display>(s: &str) -> T {
     s.parse().unwrap_or_else(|e| panic!("Invalid number {s}: {e:?}"))
 }
+
+#[cfg(not(debug_assertions))]
+pub fn parse_num<T: From<u8> + AddAssign<T> + MulAssign<T>>(s: &str) -> T {
+    let mut digits = s.bytes().map(|b| T::from(b - b'0'));
+    let mut n = digits.next().unwrap();
+    for digit in digits {
+        n *= T::from(10);
+        n += digit;
+    }
+    n
+}
diff --git a/2021/src/lib.rs b/2021/src/lib.rs
index 27a56af..456a913 100644
--- a/2021/src/lib.rs
+++ b/2021/src/lib.rs
@@ -1,2 +1,3 @@
+#![feature(associated_type_bounds)]
 pub mod common;
 pub mod teststuff;