diff --git a/2019/src/bin/puzzle_10.rs b/2019/src/bin/puzzle_10.rs
index 6fc1b33..4073176 100644
--- a/2019/src/bin/puzzle_10.rs
+++ b/2019/src/bin/puzzle_10.rs
@@ -3,6 +3,7 @@ use std::collections::HashMap;
 use std::io;
 
 use aoc2019::grid::Point;
+use aoc2019::num;
 
 #[derive(Ord, PartialOrd, Eq, PartialEq)]
 struct AsteroidMetadata {
@@ -10,14 +11,8 @@ struct AsteroidMetadata {
     distance: u32,
 }
 
-fn gcd(mut a: i32, mut b: i32) -> i32 {
-    while b != 0 {
-        let t = b;
-        b = a % b;
-        a = t;
-    }
-
-    a.abs()
+fn gcd(a: i32, b: i32) -> i32 {
+    num::gcd(a.into(), b.into()).try_into().unwrap()
 }
 
 fn distances_from(
diff --git a/2019/src/lib.rs b/2019/src/lib.rs
index be0e145..d80e898 100644
--- a/2019/src/lib.rs
+++ b/2019/src/lib.rs
@@ -1,3 +1,4 @@
 pub mod grid;
 pub mod intcode;
 pub mod iter;
+pub mod num;
diff --git a/2019/src/num.rs b/2019/src/num.rs
new file mode 100644
index 0000000..9b23186
--- /dev/null
+++ b/2019/src/num.rs
@@ -0,0 +1,9 @@
+pub fn gcd(mut a: i64, mut b: i64) -> u64 {
+    while b != 0 {
+        let t = b;
+        b = a % b;
+        a = t;
+    }
+
+    a.abs().try_into().unwrap()
+}