diff --git a/src/ciphers/aes.rs b/src/ciphers/aes.rs
index 4616966d5e4..b8cd623d291 100644
--- a/src/ciphers/aes.rs
+++ b/src/ciphers/aes.rs
@@ -303,7 +303,7 @@ fn key_expansion(init_key: &[Byte], num_rounds: usize) -> Vec<Byte> {
 
     for i in nk..nb * (nr + 1) {
         let mut temp_word = key[i - 1];
-        if i % nk == 0 {
+        if i.is_multiple_of(nk) {
             temp_word = sub_word(rot_word(temp_word), AesMode::Encryption) ^ RCON[i / nk];
         } else if nk > 6 && i % nk == 4 {
             temp_word = sub_word(temp_word, AesMode::Encryption);
diff --git a/src/data_structures/rb_tree.rs b/src/data_structures/rb_tree.rs
index df7d09cb006..5cb6316b150 100644
--- a/src/data_structures/rb_tree.rs
+++ b/src/data_structures/rb_tree.rs
@@ -367,6 +367,12 @@ unsafe fn delete_fixup<K: Ord, V>(tree: &mut RBTree<K, V>, mut parent: *mut RBNo
     let mut sr: *mut RBNode<K, V>;
 
     loop {
+        // rb-tree will keep color balance up to root,
+        // if parent is null, we are done.
+        if parent.is_null() {
+            break;
+        }
+
         /*
          * Loop invariants:
          * - node is black (or null on first iteration)
@@ -647,4 +653,23 @@ mod tests {
         let s: String = tree.iter().map(|x| x.value).collect();
         assert_eq!(s, "hlo orl!");
     }
+
+    #[test]
+    fn delete_edge_case_null_pointer_guard() {
+        let mut tree = RBTree::<i8, i8>::new();
+        tree.insert(4, 4);
+        tree.insert(2, 2);
+        tree.insert(5, 5);
+        tree.insert(0, 0);
+        tree.insert(3, 3);
+        tree.insert(-1, -1);
+        tree.insert(1, 1);
+        tree.insert(-2, -2);
+        tree.insert(6, 6);
+        tree.insert(7, 7);
+        tree.insert(8, 8);
+        tree.delete(&1);
+        tree.delete(&3);
+        tree.delete(&-1);
+    }
 }
diff --git a/src/general/permutations/steinhaus_johnson_trotter.rs b/src/general/permutations/steinhaus_johnson_trotter.rs
index 4784a927ccc..b605ce96a05 100644
--- a/src/general/permutations/steinhaus_johnson_trotter.rs
+++ b/src/general/permutations/steinhaus_johnson_trotter.rs
@@ -8,7 +8,7 @@ pub fn steinhaus_johnson_trotter_permute<T: Clone>(array: &[T]) -> Vec<Vec<T>> {
     res.push(array.clone());
     while i < len {
         if inversion_vector[i] < i {
-            if i % 2 == 0 {
+            if i.is_multiple_of(2) {
                 array.swap(0, i);
             } else {
                 array.swap(inversion_vector[i], i);
diff --git a/src/math/prime_numbers.rs b/src/math/prime_numbers.rs
index f045133a168..a1cf41d4012 100644
--- a/src/math/prime_numbers.rs
+++ b/src/math/prime_numbers.rs
@@ -9,7 +9,7 @@ pub fn prime_numbers(max: usize) -> Vec<usize> {
         let mut status = true;
 
         for j in (3..stop).step_by(2) {
-            if i % j == 0 {
+            if i.is_multiple_of(j) {
                 status = false;
                 break;
             }