diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 38fc09fc..81554b74 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -14,9 +14,11 @@ license = "GPL-3.0"
 chrono = "0.4.38"
 itertools = "0.13.0"
 num-traits = "0.2.19"
-rstest = "0.21.0"
 seq-macro = "0.3.5"
 
+[dev-dependencies]
+rstest = "0.21.0"
+
 [target.'cfg(any(target_arch="wasm32",target_arch="wasm64"))'.dependencies]
 js-sys = "0.3"
 wasm-bindgen = "0.2"
diff --git a/rust/src/include/factors.rs b/rust/src/include/factors.rs
index b322d3ba..6896ec5e 100644
--- a/rust/src/include/factors.rs
+++ b/rust/src/include/factors.rs
@@ -8,6 +8,7 @@ use itertools::Itertools;
 
 use crate::include::primes::prime_factors;
 
+#[derive(Clone, Debug)]
 pub struct ProperDivisors<I>
 {
     seen: HashSet<I>,
diff --git a/rust/src/include/fibonacci.rs b/rust/src/include/fibonacci.rs
index 0bdba578..5a033013 100644
--- a/rust/src/include/fibonacci.rs
+++ b/rust/src/include/fibonacci.rs
@@ -12,6 +12,7 @@ pub fn fib_by_3<I>() -> impl Iterator<Item = I> where I: Copy + Zero + One + Add
     return cache_iterator(FibonacciBy3::<I>::new());
 }
 
+#[derive(Clone, Copy, Debug, Hash)]
 pub struct Fibonacci<I> {
     a: I,
     b: I,
@@ -44,6 +45,7 @@ impl<I> Iterator for Fibonacci<I> where I: Zero + One + Add + Copy {
     }
 }
 
+#[derive(Clone, Copy, Debug, Hash)]
 pub struct FibonacciBy3<I> {
     a: I,
     b: I,
diff --git a/rust/src/include/iter_cache.rs b/rust/src/include/iter_cache.rs
index c1c8d74c..75418726 100644
--- a/rust/src/include/iter_cache.rs
+++ b/rust/src/include/iter_cache.rs
@@ -14,6 +14,7 @@ where
     return CachingIterator::new(iterator);
 }
 
+#[derive(Clone, Copy, Debug, Hash)]
 pub struct CachingIterator<I, T>
 where
     I: Iterator<Item = T> + 'static,
diff --git a/rust/src/include/math.rs b/rust/src/include/math.rs
index 8e085cf2..e3a2c84a 100644
--- a/rust/src/include/math.rs
+++ b/rust/src/include/math.rs
@@ -1,8 +1,10 @@
 use std::cmp::PartialOrd;
+use std::fmt::Debug;
 use std::mem::size_of;
 
 use num_traits::NumAssign;
 use num_traits::one;
+use num_traits::CheckedMul;
 
 const MAX_FACTORIAL: [u8; 16] = [
     5, // u8
@@ -23,7 +25,7 @@ where I: NumAssign + From<u8>
 }
 
 pub fn n_choose_r<I>(n: usize, r: usize) -> I
-where I: Copy + From<u8> + From<u64> + NumAssign + PartialOrd
+where I: Copy + From<u8> + From<u64> + NumAssign + PartialOrd + CheckedMul + Debug
 {
     if n < r {
         panic!("Out of function's bounds");
@@ -33,7 +35,6 @@ where I: Copy + From<u8> + From<u64> + NumAssign + PartialOrd
     }
     // slow path for larger numbers
     let mut answer: I = one();
-    let mut tmp: I;
     let mut factors: Vec<i8> = vec![1; n + 1];
     factors[0] = 0;
     factors[1] = 0;
@@ -59,17 +60,17 @@ where I: Copy + From<u8> + From<u64> + NumAssign + PartialOrd
     let mut j: usize = 2;
     while i <= n {
         while factors[i] > 0 {
-            tmp = answer;
-            answer *= (i as u64).into();
-            while answer < tmp && j <= n {
+            let mut result = answer.checked_mul(&(i as u64).into());
+            while result.is_none() && j <= n {
                 while factors[j] < 0 {
-                    tmp /= (j as u64).into();
+                    answer /= (j as u64).into();
                     factors[j] += 1;
                 }
                 j += 1;
-                answer = tmp * (i as u64).into();
+                result = answer.checked_mul(&(i as u64).into());
             }
             factors[i] -= 1;
+            answer = result.unwrap_or_else(|| panic!("nCr overflow: {:?} * {}", answer, i));
         }
         i += 1;
     }
diff --git a/rust/src/include/primes.rs b/rust/src/include/primes.rs
index aae3bd49..03b1ff6d 100644
--- a/rust/src/include/primes.rs
+++ b/rust/src/include/primes.rs
@@ -7,6 +7,7 @@ use num_traits::{one,zero,One,Zero};
 
 use crate::include::iter_cache::cache_iterator;
 
+#[derive(Clone, Debug)]
 pub struct Eratosthenes<I> where I: Hash {
     sieve: HashMap<I, Vec<I>>,
     prime: I,
@@ -68,6 +69,7 @@ pub fn primes_until<I>(x: I) -> impl Iterator<Item = I> where I: Hash + One + Ze
     return primes::<I>().take_while(move |n| *n < x);
 }
 
+#[derive(Clone, Copy, Debug, Hash)]
 pub struct PrimeFactors<I> {
     number: I
 }
diff --git a/rust/src/main.rs b/rust/src/main.rs
index e1de2135..7b83149b 100644
--- a/rust/src/main.rs
+++ b/rust/src/main.rs
@@ -15,6 +15,8 @@ use itertools::Itertools;
 pub mod include;
 use include::primes;
 use include::factors;
+#[cfg(test)]
+use include::math;
 #[cfg(not(test))]
 use include::problems::generate_supported_problems;
 use include::problems::get_problem;
@@ -150,3 +152,14 @@ fn test_proper_divisors() -> Result<(), String> {
     }
     Ok(())
 }
+
+#[cfg(test)]
+#[test]
+fn test_n_choose_r() -> Result<(), String> {
+    for i in 0..68usize {
+        for j in 0..i {
+            assert_eq!((0..i).combinations(j).count() as u128, math::n_choose_r::<u128>(i, j));
+        }
+    }
+    Ok(())
+}
diff --git a/rust/src/p0053.rs b/rust/src/p0053.rs
index 5b889496..fce64a5a 100644
--- a/rust/src/p0053.rs
+++ b/rust/src/p0053.rs
@@ -31,7 +31,7 @@ pub fn p0053() -> Answer {
     let mut answer: u64 = 0;
     for n in 1..101 {
         for r in 2..(n-1) {
-            if n_choose_r::<u64>(n, r) > 1_000_000 {
+            if n_choose_r::<u128>(n, r) > 1_000_000 {
                 answer += 1;
             }
         }