diff --git a/src/lib.rs b/src/lib.rs
index 091e8b6..4c7289a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -126,8 +126,6 @@ impl Add<SmallUint> for SmallUint {
                 match i.overflowing_add(j) {
                     (t, false) => Self(SmallUintType::Inline(t)),
                     (t, true) => {
-
-
                         let mut res = [0, 0, 0, 0, 1];
 
                         let mut v = t;
@@ -138,7 +136,9 @@ impl Add<SmallUint> for SmallUint {
                             v >>= 32;
                         }
 
-                        Self(SmallUintType::Heap((<Box<[u32]>>::from(res).as_mut_ptr(), 5)))
+                        let mut slice = ManuallyDrop::new(<Box<[u32]>>::from(res));
+
+                        Self(SmallUintType::Heap((slice.as_mut_ptr(), 5)))
 
                     }
                 }
@@ -146,7 +146,7 @@ impl Add<SmallUint> for SmallUint {
             (&SmallUintType::Heap((r, s)), &SmallUintType::Inline(i)) | (&SmallUintType::Inline(i), &SmallUintType::Heap((r, s))) => {
                 let slice1 = unsafe { core::slice::from_raw_parts(r, s) };
 
-                let mut res = [0, 0, 0, 0, 1];
+                let mut res = [0, 0, 0, 0];
 
                 let mut v = i;
                 #[allow(clippy::needless_range_loop)]
@@ -155,6 +155,7 @@ impl Add<SmallUint> for SmallUint {
 
                     v >>= 32;
                 }
+
                 let result = add_two_slices(slice1, &res[..]);
                 let size = result.len();
 
@@ -181,6 +182,7 @@ impl Add<SmallUint> for SmallUint {
     }
 }
 
+
 impl Drop for SmallInt {
     fn drop(&mut self) {
         if let Self(SmallIntType::Heap((r, s))) = self {
@@ -429,7 +431,7 @@ mod conversion_tests {
     use crate::SmallUint;
 
     #[cfg(feature = "num-bigint")]
-    use num_bigint::{BigInt, Sign, BigUint, };
+    use num_bigint::{BigInt, Sign, BigUint};
 
     macro_rules! conversion_tests {
         ($t:ty, $i:ident) => {
@@ -461,11 +463,19 @@ mod conversion_tests {
     #[cfg(feature = "num-bigint")]
     fn test_op_add_u_u() {
         let i = SmallUint::from(u128::MAX);
-        let k = SmallUint::from(&BigUint::new(vec![5, 4, 9, 3, 2, 1, 5]));
+        let k = SmallUint::from(u128::MAX);
         let q = i + k;
-        println!("{:?}", BigUint::from(&q));
-        println!("{:?}", BigUint::new(vec![5, 4, 9, 3, 2, 1, 5]) + u128::MAX);
+        assert_eq!(BigUint::from(&q), BigUint::from(u128::MAX) + u128::MAX);
 
+        let i = SmallUint::from(u128::MAX);
+        let k = SmallUint::from(&BigUint::new(vec![5, 4, 9, 3, 1, 81]));
+        let q = i + k;
+        assert_eq!(BigUint::from(&q), BigUint::new(vec![5, 4, 9, 3, 1, 81]) + u128::MAX);
+
+        let i = SmallUint::from(&BigUint::new(vec![3, 9, 8]));
+        let k = SmallUint::from(&BigUint::new(vec![5, 4, 9, 3, 1, 81]));
+        let q = i + k;
+        assert_eq!(BigUint::from(&q), BigUint::new(vec![3, 9, 8]) + BigUint::new(vec![5, 4, 9, 3, 1, 81]));
     }
 
     #[test]