diff --git a/soroban-sdk/src/num.rs b/soroban-sdk/src/num.rs
index 55ae4156e..fcdb39c00 100644
--- a/soroban-sdk/src/num.rs
+++ b/soroban-sdk/src/num.rs
@@ -206,8 +206,7 @@ impl U256 {
     pub const BITS: u32 = 256;
 
     fn is_zero(&self) -> bool {
-        const ZERO: U256Val = U256Val::from_u32(0);
-        self.val.as_val().get_payload() == ZERO.as_val().get_payload()
+        *self == U256::from_u32(&self.env, 0)
     }
 
     pub fn from_u32(env: &Env, u: u32) -> Self {
@@ -440,13 +439,11 @@ impl I256 {
     pub const BITS: u32 = 256;
 
     fn is_zero(&self) -> bool {
-        const ZERO: I256Val = I256Val::from_i32(0);
-        self.val.as_val().get_payload() == ZERO.as_val().get_payload()
+        *self == I256::from_i32(&self.env, 0)
     }
 
     fn is_neg_one(&self) -> bool {
-        const NEG_ONE: I256Val = I256Val::from_i32(-1);
-        self.val.as_val().get_payload() == NEG_ONE.as_val().get_payload()
+        *self == I256::from_i32(&self.env, -1)
     }
 
     /// Returns the minimum value of I256 (-2^255).
@@ -850,6 +847,61 @@ mod test {
         assert_eq!(u3.rem_euclid(&u4), U256::from_u32(&env, 3));
     }
 
+    #[test]
+    fn test_u256_checked_arith() {
+        let env = Env::default();
+
+        let u1 = U256::from_u32(&env, 6);
+        let u2 = U256::from_u32(&env, 3);
+        assert_eq!(u1.checked_add(&u2), Some(U256::from_u32(&env, 9)));
+        assert_eq!(u1.checked_sub(&u2), Some(U256::from_u32(&env, 3)));
+        assert_eq!(u1.checked_mul(&u2), Some(U256::from_u32(&env, 18)));
+        assert_eq!(u1.checked_div(&u2), Some(U256::from_u32(&env, 2)));
+        assert_eq!(u1.checked_pow(2), Some(U256::from_u32(&env, 36)));
+        assert_eq!(u1.checked_shl(2), Some(U256::from_u32(&env, 24)));
+        assert_eq!(u1.checked_shr(1), Some(U256::from_u32(&env, 3)));
+
+        let u3 = U256::from_u32(&env, 7);
+        let u4 = U256::from_u32(&env, 4);
+        assert_eq!(u3.checked_rem_euclid(&u4), Some(U256::from_u32(&env, 3)));
+    }
+
+    #[test]
+    fn test_u256_checked_arith_overflow() {
+        let env = Env::default();
+
+        let zero = U256::from_u32(&env, 0);
+        let one = U256::from_u32(&env, 1);
+        let two = U256::from_u32(&env, 2);
+        let max = U256::from_parts(&env, u64::MAX, u64::MAX, u64::MAX, u64::MAX);
+        assert_eq!(max.checked_add(&one), None);
+        assert_eq!(zero.checked_sub(&one), None);
+        assert_eq!(max.checked_mul(&two), None);
+        assert_eq!(one.checked_div(&zero), None);
+        assert_eq!(max.checked_pow(2), None);
+        assert_eq!(one.checked_shl(256), None);
+        assert_eq!(one.checked_shr(256), None);
+        assert_eq!(one.checked_rem_euclid(&zero), None);
+
+        let zero_from_parts = U256::from_parts(&env, 0, 0, 0, 0);
+        let one_from_parts = U256::from_parts(&env, 0, 0, 0, 1);
+        assert_eq!(one.checked_div(&zero_from_parts), None);
+        assert_eq!(zero.checked_sub(&one_from_parts), None);
+    }
+
+    #[test]
+    fn test_u256_is_zero() {
+        let env = Env::default();
+
+        let zero = U256::from_u32(&env, 0);
+        let zero_from_parts = U256::from_parts(&env, 0, 0, 0, 0);
+        let non_zero = U256::from_u32(&env, 1);
+
+        assert!(zero.is_zero());
+        assert!(zero_from_parts.is_zero());
+        assert!(!non_zero.is_zero());
+    }
+
     #[test]
     fn test_i256_arith() {
         let env = Env::default();
@@ -868,4 +920,89 @@ mod test {
         let u4 = I256::from_i32(&env, 4);
         assert_eq!(u3.rem_euclid(&u4), I256::from_i32(&env, 1));
     }
+
+    #[test]
+    fn test_i256_checked_arith() {
+        let env = Env::default();
+
+        let i1 = I256::from_i32(&env, -6);
+        let i2 = I256::from_i32(&env, 3);
+        assert_eq!(i1.checked_add(&i2), Some(I256::from_i32(&env, -3)));
+        assert_eq!(i1.checked_sub(&i2), Some(I256::from_i32(&env, -9)));
+        assert_eq!(i1.checked_mul(&i2), Some(I256::from_i32(&env, -18)));
+        assert_eq!(i1.checked_div(&i2), Some(I256::from_i32(&env, -2)));
+        assert_eq!(i1.checked_pow(2), Some(I256::from_i32(&env, 36)));
+        assert_eq!(i1.checked_shl(2), Some(I256::from_i32(&env, -24)));
+        assert_eq!(i1.checked_shr(1), Some(I256::from_i32(&env, -3)));
+
+        let u3 = I256::from_i32(&env, -7);
+        let u4 = I256::from_i32(&env, 4);
+        assert_eq!(u3.checked_rem_euclid(&u4), Some(I256::from_i32(&env, 1)));
+    }
+
+    #[test]
+    fn test_i256_checked_arith_overflow() {
+        let env = Env::default();
+
+        let zero = I256::from_i32(&env, 0);
+        let one = I256::from_i32(&env, 1);
+        let negative_one = I256::from_i32(&env, -1);
+        let two = I256::from_i32(&env, 2);
+        let max = I256::from_parts(&env, i64::MAX, u64::MAX, u64::MAX, u64::MAX);
+        let min = I256::from_parts(&env, i64::MIN, 0, 0, 0);
+        assert_eq!(max.checked_add(&one), None);
+        assert_eq!(min.checked_sub(&one), None);
+        assert_eq!(max.checked_mul(&two), None);
+        assert_eq!(one.checked_div(&zero), None);
+        assert_eq!(min.checked_div(&negative_one), None);
+        assert_eq!(max.checked_pow(2), None);
+        assert_eq!(one.checked_shl(256), None);
+        assert_eq!(one.checked_shr(256), None);
+        assert_eq!(one.checked_rem_euclid(&zero), None);
+
+        let zero_from_parts = I256::from_parts(&env, 0, 0, 0, 0);
+        let one_from_parts = I256::from_parts(&env, 0, 0, 0, 1);
+        assert_eq!(one.checked_div(&zero_from_parts), None);
+        assert_eq!(min.checked_sub(&one_from_parts), None);
+    }
+
+    #[test]
+    fn test_i256_is_zero() {
+        let env = Env::default();
+
+        let zero = I256::from_i32(&env, 0);
+        let zero_from_parts = I256::from_parts(&env, 0, 0, 0, 0);
+        let non_zero = I256::from_i32(&env, 1);
+
+        assert!(zero.is_zero());
+        assert!(zero_from_parts.is_zero());
+        assert!(!non_zero.is_zero());
+    }
+
+    #[test]
+    fn test_i256_is_neg_one() {
+        let env = Env::default();
+
+        let negative_one = I256::from_i32(&env, -1);
+        let negative_one_from_parts = I256::from_parts(&env, -1, u64::MAX, u64::MAX, u64::MAX);
+        let negative_two = I256::from_i32(&env, -2);
+
+        assert!(negative_one.is_neg_one());
+        assert!(negative_one_from_parts.is_neg_one());
+        assert!(!negative_two.is_neg_one());
+    }
+
+    #[test]
+    fn test_i256_is_div_overflow() {
+        let env = Env::default();
+
+        let zero = I256::from_i32(&env, 0);
+        let negative_one = I256::from_i32(&env, -1);
+        let min = I256::min_value(&env);
+
+        assert!(!zero.is_div_overflow(&negative_one));
+
+        assert!(negative_one.is_div_overflow(&zero));
+        assert!(min.is_div_overflow(&negative_one));
+    }
 }