diff --git a/src/day09/errors.rs b/src/day09/errors.rs
new file mode 100644
index 0000000..6804f9c
--- /dev/null
+++ b/src/day09/errors.rs
@@ -0,0 +1,13 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum Errors {
+    #[error("invalid input")]
+    InvalidInput,
+}
+
+impl From<std::num::ParseIntError> for Errors {
+    fn from(_: std::num::ParseIntError) -> Self {
+        Errors::InvalidInput
+    }
+}
diff --git a/src/day09/main.rs b/src/day09/main.rs
index 6db5201..1838bd3 100644
--- a/src/day09/main.rs
+++ b/src/day09/main.rs
@@ -1,11 +1,13 @@
 use anyhow::Result;
 use std::convert::TryFrom;
-use thiserror::Error;
+
+pub mod xmas_decoder;
+pub mod errors;
 
 static INPUT: &str = include_str!("../../input09");
 
 fn main() -> Result<()> {
-    let decoder = XMASDecoder::try_from(INPUT)?;
+    let decoder = xmas_decoder::XMASDecoder::try_from(INPUT)?;
 
     let missing = decoder.decode().expect("did not find a solution");
     println!("missing: {}", missing);
@@ -19,77 +21,3 @@ fn main() -> Result<()> {
     Ok(())
 }
 
-pub struct XMASDecoder {
-    input: Vec<i64>,
-}
-
-impl TryFrom<&str> for XMASDecoder {
-    type Error = Errors;
-
-    fn try_from(input: &str) -> Result<Self, Self::Error> {
-        let input = input
-            .split_ascii_whitespace()
-            .map(|line| line.trim().parse::<i64>())
-            .collect::<std::result::Result<Vec<i64>, _>>()?;
-        Ok(Self { input })
-    }
-}
-
-impl XMASDecoder {
-    pub fn find_continues(&self, target: i64) -> Option<&[i64]> {
-        for offset in 0..self.input.len() {
-            let slice = &self.input[offset..self.input.len()];
-            if let Some(found) = Self::find_sum_slice(slice, target) {
-                return Some(found);
-            }
-        }
-        None
-    }
-
-    fn find_sum_slice(slice: &[i64], target: i64) -> Option<&[i64]> {
-        let mut offset = 0;
-        let mut sum = 0;
-        for i in slice {
-            offset += 1;
-            sum += *i;
-            if sum == target {
-                return Some(&slice[0..offset]);
-            } else if sum > target {
-                return None;
-            }
-        }
-        None
-    }
-
-    pub fn decode(&self) -> Option<i64> {
-        self.input
-            .windows(26)
-            .into_iter()
-            .filter_map(Self::validate_slice)
-            .next()
-    }
-
-    fn validate_slice(window: &[i64]) -> Option<i64> {
-        let (target, slice) = window.split_last().unwrap();
-        for (offset, a) in slice.iter().enumerate() {
-            for b in slice[offset + 1..slice.len()].iter() {
-                if a + b == *target {
-                    return None;
-                }
-            }
-        }
-        Some(*target)
-    }
-}
-
-#[derive(Error, Debug)]
-pub enum Errors {
-    #[error("invalid input")]
-    InvalidInput,
-}
-
-impl From<std::num::ParseIntError> for Errors {
-    fn from(_: std::num::ParseIntError) -> Self {
-        Errors::InvalidInput
-    }
-}
diff --git a/src/day09/xmas_decoder.rs b/src/day09/xmas_decoder.rs
new file mode 100644
index 0000000..355192c
--- /dev/null
+++ b/src/day09/xmas_decoder.rs
@@ -0,0 +1,65 @@
+use std::convert::TryFrom;
+use super::errors;
+
+pub struct XMASDecoder {
+    input: Vec<i64>,
+}
+
+impl TryFrom<&str> for XMASDecoder {
+    type Error = errors::Errors;
+
+    fn try_from(input: &str) -> Result<Self, Self::Error> {
+        let input = input
+            .split_ascii_whitespace()
+            .map(|line| line.trim().parse::<i64>())
+            .collect::<std::result::Result<Vec<i64>, _>>()?;
+        Ok(Self { input })
+    }
+}
+
+impl XMASDecoder {
+    pub fn find_continues(&self, target: i64) -> Option<&[i64]> {
+        for offset in 0..self.input.len() {
+            let slice = &self.input[offset..self.input.len()];
+            if let Some(found) = Self::find_sum_slice(slice, target) {
+                return Some(found);
+            }
+        }
+        None
+    }
+
+    fn find_sum_slice(slice: &[i64], target: i64) -> Option<&[i64]> {
+        let mut offset = 0;
+        let mut sum = 0;
+        for i in slice {
+            offset += 1;
+            sum += *i;
+            if sum == target {
+                return Some(&slice[0..offset]);
+            } else if sum > target {
+                return None;
+            }
+        }
+        None
+    }
+
+    pub fn decode(&self) -> Option<i64> {
+        self.input
+            .windows(26)
+            .into_iter()
+            .filter_map(Self::validate_slice)
+            .next()
+    }
+
+    fn validate_slice(window: &[i64]) -> Option<i64> {
+        let (target, slice) = window.split_last().unwrap();
+        for (offset, a) in slice.iter().enumerate() {
+            for b in slice[offset + 1..slice.len()].iter() {
+                if a + b == *target {
+                    return None;
+                }
+            }
+        }
+        Some(*target)
+    }
+}