diff --git a/README.md b/README.md
index 4a293fd..f277a54 100644
--- a/README.md
+++ b/README.md
@@ -17,7 +17,7 @@
 | 6   | [src/solutions/day06.rs](src/solutions/day06.rs)         | ⭐️⭐️   |
 | 7   | [src/solutions/day07.rs](src/solutions/day07.rs)         | ⭐️⭐️   |
 | 8   | [src/solutions/day08.rs](src/solutions/day08.rs)         | ⭐️⭐️   |
-<!-- | 9   | [src/solutions/day09.rs](src/solutions/day09.rs)         | ⭐️⭐️   | -->
+| 9   | [src/solutions/day09.rs](src/solutions/day09.rs)         | ⭐️⭐️   |
 <!-- | 10  | [src/solutions/day10.rs](src/solutions/day10.rs)         | ⭐️⭐️   | -->
 <!-- | 11  | [src/solutions/day11.rs](src/solutions/day11.rs)         | ⭐️⭐️   | -->
 <!-- | 12  | [src/solutions/day12.rs](src/solutions/day12.rs)         | ⭐️⭐️   | -->
diff --git a/src/solutions/day09.rs b/src/solutions/day09.rs
index e7905a3..9dbd4e2 100644
--- a/src/solutions/day09.rs
+++ b/src/solutions/day09.rs
@@ -1,6 +1,5 @@
-use std::num::ParseIntError;
-
 use crate::data::load;
+use std::num::ParseIntError;
 use thiserror::Error;
 
 #[derive(Error, Debug, PartialEq, Eq)]
@@ -48,6 +47,17 @@ pub fn puzzle_1(input: &str) -> Result<i32, PuzzleErr> {
     Ok(seqs.iter().map(|s| oasis_prediction(s)).sum())
 }
 
+pub fn puzzle_2(input: &str) -> Result<i32, PuzzleErr> {
+    let seqs = parse_input(input)?
+        .iter_mut()
+        .map(|s| {
+            s.reverse();
+            s.clone()
+        })
+        .collect::<Vec<_>>();
+    Ok(seqs.iter().map(|s| oasis_prediction(s)).sum())
+}
+
 pub fn main(data_dir: &str) {
     println!("Day 9: Mirage Maintenance");
     let data = load(data_dir, 9, None);
@@ -61,10 +71,10 @@ pub fn main(data_dir: &str) {
     assert_eq!(answer_1, Ok(1666172641));
 
     // Puzzle 2.
-    // let answer_2 = puzzle_2(&data);
-    // match answer_2 {
-    //     Ok(x) => println!(" Puzzle 2: {}", x),
-    //     Err(e) => panic!("No solution to puzzle 2: {}", e),
-    // }
-    // assert_eq!(answer_2, Ok(21003205388413))
+    let answer_2 = puzzle_2(&data);
+    match answer_2 {
+        Ok(x) => println!(" Puzzle 2: {}", x),
+        Err(e) => panic!("No solution to puzzle 2: {}", e),
+    }
+    assert_eq!(answer_2, Ok(933))
 }
diff --git a/tests/test_day09.rs b/tests/test_day09.rs
index bae4a58..03cb9f4 100644
--- a/tests/test_day09.rs
+++ b/tests/test_day09.rs
@@ -1,4 +1,4 @@
-use aoc_2023::solutions::day09::puzzle_1;
+use aoc_2023::solutions::day09::{puzzle_1, puzzle_2};
 
 const EXAMPLE_INPUT_1: &str = "
 0 3 6 9 12 15
@@ -11,3 +11,9 @@ fn example_1_puzzle_1() {
     let _ = env_logger::try_init();
     assert_eq!(puzzle_1(self::EXAMPLE_INPUT_1), Ok(114));
 }
+
+#[test]
+fn example_1_puzzle_2() {
+    let _ = env_logger::try_init();
+    assert_eq!(puzzle_2(self::EXAMPLE_INPUT_1), Ok(2));
+}