diff --git a/2023/day6/rust/src/main.rs b/2023/day6/rust/src/main.rs
index 36cbcf3..f224132 100644
--- a/2023/day6/rust/src/main.rs
+++ b/2023/day6/rust/src/main.rs
@@ -1,6 +1,16 @@
 #![warn(clippy::pedantic)]
 
-use std::io::stdin;
+use std::{io::stdin, ops::Div};
+
+#[allow(
+    clippy::cast_possible_truncation,
+    clippy::cast_sign_loss,
+    clippy::cast_precision_loss
+)]
+// FIXME: https://github.com/rust-lang/rust/issues/116226
+fn isqrt(n: u64) -> u64 {
+    (n as f64).sqrt().floor() as u64
+}
 
 fn calculate_score<I: IntoIterator<Item = (u64, u64)>>(races: I) -> u64 {
     races
@@ -11,16 +21,14 @@ fn calculate_score<I: IntoIterator<Item = (u64, u64)>>(races: I) -> u64 {
             // x^2-tx+r = 0
             // [ x^2+px+q = 0  ==>  x = -p/2±sqrt((p/2)^2-q) ]
             // x = t/2 ± sqrt(t^2/4-r)
+            // x = (t ± 2 * sqrt(t^2/4-r)) / 2
+            // x = (t ± sqrt(t^2-4r)) / 2
 
-            #[allow(clippy::cast_precision_loss)]
-            let t = t as f64;
-            #[allow(clippy::cast_precision_loss)]
-            let r = r as f64;
-
-            let v = t / 2.0;
-            let w = (t.powi(2) / 4.0 - r).sqrt();
-            #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
-            ((v - w + 1.0).floor() as u64, (v + w - 1.0).ceil() as u64)
+            let d_squared = t.pow(2) - 4 * r;
+            // add a little bias for perfect squares, and subtract 1 to get the x values that lie
+            // inside r
+            let d = isqrt(d_squared - 1) - 1;
+            ((t - d).div(2), (t + d).div_ceil(2))
         })
         .map(|(min, max)| max - min + 1)
         .product()