diff --git a/rust/grains/src/lib.rs b/rust/grains/src/lib.rs
index ab7bb6c..1681d66 100644
--- a/rust/grains/src/lib.rs
+++ b/rust/grains/src/lib.rs
@@ -1,7 +1,10 @@
 pub fn square(s: u32) -> u64 {
+    if s == 0 || s > 64 {
+        panic!("Square must be between 1 and 64");
+    }
     2_u64.pow(s - 1)
 }
 
 pub fn total() -> u64 {
-    (1..=64).map(|x| square(x)).sum()
+    (1..=64).map(square).sum()
 }