diff --git a/ceno_zkvm/src/uint/arithmetic.rs b/ceno_zkvm/src/uint/arithmetic.rs
index 1362ce74d..8a0e58f37 100644
--- a/ceno_zkvm/src/uint/arithmetic.rs
+++ b/ceno_zkvm/src/uint/arithmetic.rs
@@ -691,9 +691,20 @@ mod tests {
         use itertools::Itertools;
 
         type E = GoldilocksExt2; // 18446744069414584321
-        const POW_OF_C: u64 = 2_usize.pow(16u32) as u64;
+        // const POW_OF_C: u64 = 2_usize.pow(16u32) as u64;
+
+        // fn test_data() -> Vec<Vec<u64>> {
+        //     let d = vec![
+        //         [256, 256, 0, 0].into(),
+        //         [257, 256, 0, 0].into(),
+        //         [256, 257, 2, 1].into(),
+        //         [1, 2, 1].into(),
+        //     ];
+        //     d
+        // }
+
         #[test]
-        fn test_mul_no_carries() {
+        fn test_mul64_16_no_carries() {
             // a = 1 + 1 * 2^16
             // b = 2 + 1 * 2^16
             // c = 2 + 3 * 2^16 + 1 * 2^32 = 4,295,163,906
@@ -706,7 +717,7 @@ mod tests {
         }
 
         #[test]
-        fn test_mul_w_carry() {
+        fn test_mul64_16_w_carry() {
             // a = 256 + 1 * 2^16
             // b = 257 + 1 * 2^16
             // c = 256 + 514 * 2^16 + 1 * 2^32 = 4,328,653,056
@@ -719,7 +730,7 @@ mod tests {
         }
 
         #[test]
-        fn test_mul_w_carries() {
+        fn test_mul64_16_w_carries() {
             // a = 256 + 256 * 2^16 = 16,777,472
             // b = 257 + 256 * 2^16 = 16,777,473
             // c = 256 + 257 * 2^16 + 2 * 2^32 + 1 * 2^48 = 281,483,583,488,256
@@ -734,11 +745,50 @@ mod tests {
             verify::<64, 16, E>(witness_values, false);
         }
 
+        #[test]
+        fn test_mul64_8_w_carries() {
+            // a = 256
+            // b = 257
+            // c = 254 + 1 * 2^16 = 510
+            let wit_a = vec![255, 0, 0, 0, 0, 0, 0, 0];
+            let wit_b = vec![2, 0, 0, 0, 0, 0, 0, 0];
+            let wit_c = vec![254, 1, 0, 0, 0, 0, 0, 0];
+            let wit_carries = vec![1, 0, 0, 0, 0, 0, 0];
+            let witness_values = [wit_a, wit_b, wit_c, wit_carries].concat();
+            verify::<64, 8, E>(witness_values, false);
+        }
+
+        #[test]
+        fn test_mul32_16_w_carries() {
+            // a = 256
+            // b = 257
+            // c = 256 + 1 * 2^16 = 65,792
+            let wit_a = vec![256, 0];
+            let wit_b = vec![257, 0];
+            let wit_c = vec![256, 1];
+            let wit_carries = vec![1, 0];
+            let witness_values = [wit_a, wit_b, wit_c, wit_carries].concat();
+            verify::<32, 16, E>(witness_values, false);
+        }
+
+        #[test]
+        fn test_mul32_5_w_carries() {
+            // a = 31
+            // b = 2
+            // c = 30 + 1 * 2^8 = 62
+            let wit_a = vec![31, 0, 0, 0, 0, 0, 0];
+            let wit_b = vec![2, 0, 0, 0, 0, 0, 0];
+            let wit_c = vec![30, 1, 0, 0, 0, 0, 0];
+            let wit_carries = vec![1, 0, 0, 0, 0, 0];
+            let witness_values = [wit_a, wit_b, wit_c, wit_carries].concat();
+            verify::<32, 5, E>(witness_values, false);
+        }
+
         fn verify<const M: usize, const C: usize, E: ExtensionField>(
             witness_values: Vec<u64>,
             overflow: bool,
         ) {
-            let mut cs = ConstraintSystem::new(|| "test");
+            let mut cs = ConstraintSystem::new(|| "test_mul");
             let mut circuit_builder = CircuitBuilder::<E>::new(&mut cs);
             let challenges = (0..witness_values.len()).map(|_| 1.into()).collect_vec();
 
@@ -748,6 +798,7 @@ mod tests {
                 .mul(|| "uint_c", &mut circuit_builder, &mut uint_b, false)
                 .unwrap();
 
+            let POW_OF_C: u64 = 2_usize.pow(UInt::<M, C, E>::MAX_CELL_BIT_WIDTH as u32) as u64;
             let single_wit_size = UInt::<M, C, E>::NUM_CELLS;
             let wit_end_idx = if overflow {
                 4 * single_wit_size
@@ -767,13 +818,15 @@ mod tests {
                         result[idx] += a_limb * b_limb;
                     }
                 });
+            });
 
-                // take care carries
+            // take care carries
+            result.iter_mut().enumerate().for_each(|(i, ret)| {
                 if !overflow && c_carries.get(i).is_some() {
-                    result[i] -= c_carries[i] * POW_OF_C;
+                    *ret -= c_carries[i] * POW_OF_C;
                 }
                 if i != 0 {
-                    result[i] += c_carries[i - 1];
+                    *ret += c_carries[i - 1];
                 }
             });