diff --git a/crates/flat/src/zigzag.rs b/crates/flat/src/zigzag.rs
index ed8f3108..316a35b5 100644
--- a/crates/flat/src/zigzag.rs
+++ b/crates/flat/src/zigzag.rs
@@ -1,7 +1,7 @@
 pub fn to_usize(x: isize) -> usize {
     let double_x = x << 1;
 
-    if x >= 0 {
+    if x.is_positive() || x == 0 {
         double_x as usize
     } else {
         (-double_x - 1) as usize
@@ -9,19 +9,5 @@ pub fn to_usize(x: isize) -> usize {
 }
 
 pub fn to_isize(u: usize) -> isize {
-    let s = u as isize;
-
-    (s >> 1) ^ -(s & 1)
-}
-
-#[cfg(test)]
-mod test {
-    #[test]
-    fn convert() {
-        let n = -12;
-        let unsigned = super::to_usize(n);
-        let signed = super::to_isize(unsigned);
-
-        assert_eq!(n, signed)
-    }
+    ((u >> 1) as isize) ^ (-((u & 1) as isize))
 }