diff --git a/src/sphere.rs b/src/sphere.rs
index b1c5977..17beb81 100644
--- a/src/sphere.rs
+++ b/src/sphere.rs
@@ -27,9 +27,9 @@ impl Hittable for Sphere {
         let sqrtd = discriminant.sqrt();
         
         // nearest root that lies within tolerance
-        let root = (-half_b - sqrtd) / a;
+        let mut root = (-half_b - sqrtd) / a;
         if root < t_min || root > t_max {
-            let root = (-half_b + sqrtd) / a;
+            root = (-half_b + sqrtd) / a;
             if root < t_min || root > t_max {
                 return None;
             }