diff --git a/src/coprocessor/codec/convert.rs b/src/coprocessor/codec/convert.rs
index 9c66be9e1691..fab67b531346 100644
--- a/src/coprocessor/codec/convert.rs
+++ b/src/coprocessor/codec/convert.rs
@@ -151,7 +151,7 @@ pub fn convert_bytes_to_int(ctx: &mut EvalContext, bytes: &[u8], tp: FieldTypeTp
         Ok(val) => convert_int_to_int(ctx, val, tp),
         Err(_) => {
             ctx.handle_overflow(Error::overflow("BIGINT", &vs))?;
-            let val = if vs.starts_with("-") {
+            let val = if vs.starts_with('-') {
                 integer_signed_lower_bound(tp)
             } else {
                 integer_signed_upper_bound(tp)