diff --git a/bus-mapping/src/circuit_input_builder.rs b/bus-mapping/src/circuit_input_builder.rs
index 8c45839a7b..c370c3cbf7 100644
--- a/bus-mapping/src/circuit_input_builder.rs
+++ b/bus-mapping/src/circuit_input_builder.rs
@@ -678,7 +678,7 @@ impl<'a> CircuitInputBuilder {
                     )
                 } else {
                     let stack_input_num = 1024 - geth_step.op.valid_stack_ptr_range().1 as usize;
-                    (0..stack_input_num).into_iter().map(|i|
+                    (0..stack_input_num).map(|i|
                         format!("{:?}",  geth_step.stack.nth_last(i))
                     ).collect_vec().join(" ")
                 }
diff --git a/bus-mapping/src/circuit_input_builder/input_state_ref.rs b/bus-mapping/src/circuit_input_builder/input_state_ref.rs
index ab8479a68a..a5615573da 100644
--- a/bus-mapping/src/circuit_input_builder/input_state_ref.rs
+++ b/bus-mapping/src/circuit_input_builder/input_state_ref.rs
@@ -1346,7 +1346,7 @@ impl<'a> CircuitInputStateRef<'a> {
     ) -> Result<(), Error> {
         let call = self.call()?.clone();
         let geth_step = steps
-            .get(0)
+            .first()
             .ok_or(Error::InternalError("invalid index 0"))?;
         let is_err = exec_step.error.is_some();
         let is_return_revert_succ = (geth_step.op == OpcodeId::REVERT
@@ -1516,7 +1516,7 @@ impl<'a> CircuitInputStateRef<'a> {
 
         let call = self.call()?;
 
-        if matches!(next_step, None) {
+        if next_step.is_none() {
             // enumerating call scope successful cases
             // case 1: call with normal halt opcode termination
             if matches!(
diff --git a/bus-mapping/src/circuit_input_builder/l2.rs b/bus-mapping/src/circuit_input_builder/l2.rs
index 117cea4084..05935e290b 100644
--- a/bus-mapping/src/circuit_input_builder/l2.rs
+++ b/bus-mapping/src/circuit_input_builder/l2.rs
@@ -395,8 +395,8 @@ impl CircuitInputBuilder {
                 !existed
             }),
         )
-        .fold(
-            Ok(HashMap::new()),
+        .try_fold(
+            HashMap::new(),
             |m, parsed| -> Result<HashMap<_, _>, Error> {
                 let mut m = m?;
                 let (addr, acc) = parsed.map_err(Error::IoError)?;
@@ -415,8 +415,8 @@ impl CircuitInputBuilder {
                 !existed
             }),
         )
-        .fold(
-            Ok(HashMap::new()),
+        .try_fold(
+            HashMap::new(),
             |m, parsed| -> Result<HashMap<(Address, Word), Word>, Error> {
                 let mut m = m?;
                 let ((addr, key), val) = parsed.map_err(Error::IoError)?;