diff --git a/crates/perry-codegen/src/collectors/pointer_locals.rs b/crates/perry-codegen/src/collectors/pointer_locals.rs
index 5b5abf5c5..f991b596e 100644
--- a/crates/perry-codegen/src/collectors/pointer_locals.rs
+++ b/crates/perry-codegen/src/collectors/pointer_locals.rs
@@ -192,6 +192,7 @@ pub fn collect_pointer_typed_locals(
             | Expr::BufferFrom { .. }
             | Expr::BufferFromArrayBuffer { .. }
             | Expr::BufferConcat(_)
+            | Expr::BufferConcatWithLength { .. }
             | Expr::Uint8ArrayNew(_)
             | Expr::Uint8ArrayFrom(_)
             | Expr::TextEncoderEncode(_) => Some(Type::Named("Uint8Array".into())),
diff --git a/crates/perry-codegen/src/expr/array_methods.rs b/crates/perry-codegen/src/expr/array_methods.rs
index bad0f883e..86afcc358 100644
--- a/crates/perry-codegen/src/expr/array_methods.rs
+++ b/crates/perry-codegen/src/expr/array_methods.rs
@@ -143,6 +143,18 @@ pub(crate) fn lower(ctx: &mut FnCtx<'_>, expr: &Expr) -> Result<String> {
             let buf_handle = blk.call(I64, "js_buffer_concat", &[(I64, &arr_handle)]);
             Ok(nanbox_pointer_inline(blk, &buf_handle))
         }
+        Expr::BufferConcatWithLength { list, total_length } => {
+            let arr_box = lower_expr(ctx, list)?;
+            let total_box = lower_expr(ctx, total_length)?;
+            let blk = ctx.block();
+            let arr_handle = unbox_to_i64(blk, &arr_box);
+            let buf_handle = blk.call(
+                I64,
+                "js_buffer_concat_with_length",
+                &[(I64, &arr_handle), (DOUBLE, &total_box)],
+            );
+            Ok(nanbox_pointer_inline(blk, &buf_handle))
+        }
 
         // #1177: `buf.slice(start?, end?)` on a statically buffer-producing
         // receiver — emitted by the HIR fold at `expr_call/mod.rs:5396` when
diff --git a/crates/perry-codegen/src/expr/calls.rs b/crates/perry-codegen/src/expr/calls.rs
index 5194191e7..2ddea5799 100644
--- a/crates/perry-codegen/src/expr/calls.rs
+++ b/crates/perry-codegen/src/expr/calls.rs
@@ -60,6 +60,7 @@ fn hash_input_is_buffer(ctx: &FnCtx<'_>, e: &Expr) -> bool {
             | Expr::BufferAlloc { .. }
             | Expr::BufferAllocUnsafe(_)
             | Expr::BufferConcat(_)
+            | Expr::BufferConcatWithLength { .. }
             | Expr::CryptoRandomBytes(_)
     ) {
         return true;
diff --git a/crates/perry-codegen/src/expr/mod.rs b/crates/perry-codegen/src/expr/mod.rs
index 6f994018e..f4f83c5d1 100644
--- a/crates/perry-codegen/src/expr/mod.rs
+++ b/crates/perry-codegen/src/expr/mod.rs
@@ -1745,6 +1745,7 @@ pub(crate) fn lower_expr(ctx: &mut FnCtx<'_>, expr: &Expr) -> Result<String> {
         | Expr::AggregateErrorNew { .. }
         | Expr::RegExpLastIndex(..)
         | Expr::BufferConcat(..)
+        | Expr::BufferConcatWithLength { .. }
         | Expr::BufferSlice { .. }
         | Expr::BufferIsBuffer(..)
         | Expr::BufferIsEncoding(..)
diff --git a/crates/perry-codegen/src/runtime_decls/stdlib_ffi.rs b/crates/perry-codegen/src/runtime_decls/stdlib_ffi.rs
index 55aee1bc6..fdf5d2d67 100644
--- a/crates/perry-codegen/src/runtime_decls/stdlib_ffi.rs
+++ b/crates/perry-codegen/src/runtime_decls/stdlib_ffi.rs
@@ -406,6 +406,7 @@ pub fn declare_stdlib_ffi(module: &mut LlModule) {
     module.declare_function("js_buffer_byte_length", I32, &[I64]);
     module.declare_function("js_buffer_byte_length_value", I32, &[DOUBLE, DOUBLE]);
     module.declare_function("js_buffer_concat", I64, &[I64]);
+    module.declare_function("js_buffer_concat_with_length", I64, &[I64, DOUBLE]);
     module.declare_function("js_buffer_copy", I32, &[I64, I64, I32, I32, I32]);
     module.declare_function("js_buffer_equals", I32, &[I64, I64]);
     module.declare_function("js_buffer_fill", I64, &[I64, I32]);
diff --git a/crates/perry-codegen/src/type_analysis.rs b/crates/perry-codegen/src/type_analysis.rs
index 49cd56704..57e39c863 100644
--- a/crates/perry-codegen/src/type_analysis.rs
+++ b/crates/perry-codegen/src/type_analysis.rs
@@ -230,6 +230,7 @@ pub(crate) fn refine_type_from_init(ctx: &FnCtx<'_>, init: &Expr) -> Option<HirT
         | Expr::BufferAlloc { .. }
         | Expr::BufferAllocUnsafe(_)
         | Expr::BufferConcat(_)
+        | Expr::BufferConcatWithLength { .. }
         | Expr::CryptoRandomBytes(_) => Some(HirType::Named("Uint8Array".into())),
         // Compare results are now NaN-boxed booleans (TAG_TRUE/FALSE).
         // Type-refining the local as Boolean lets is_numeric_expr
diff --git a/crates/perry-hir/src/analysis.rs b/crates/perry-hir/src/analysis.rs
index 1762805cf..5a6cc2470 100644
--- a/crates/perry-hir/src/analysis.rs
+++ b/crates/perry-hir/src/analysis.rs
@@ -748,6 +748,10 @@ pub(crate) fn collect_assigned_locals_expr(expr: &Expr, assigned: &mut Vec<Local
         | Expr::BufferLength(expr) => {
             collect_assigned_locals_expr(expr, assigned);
         }
+        Expr::BufferConcatWithLength { list, total_length } => {
+            collect_assigned_locals_expr(list, assigned);
+            collect_assigned_locals_expr(total_length, assigned);
+        }
         Expr::BufferByteLength { data, encoding } => {
             collect_assigned_locals_expr(data, assigned);
             if let Some(enc) = encoding {
diff --git a/crates/perry-hir/src/ir/expr.rs b/crates/perry-hir/src/ir/expr.rs
index ecb0db462..541f80ad9 100644
--- a/crates/perry-hir/src/ir/expr.rs
+++ b/crates/perry-hir/src/ir/expr.rs
@@ -982,8 +982,13 @@ pub enum Expr {
     },
     BufferAllocUnsafe(Box<Expr>), // Buffer.allocUnsafe(size) -> Buffer
     BufferConcat(Box<Expr>),      // Buffer.concat(list) -> Buffer
-    BufferIsBuffer(Box<Expr>),    // Buffer.isBuffer(obj) -> boolean
-    BufferIsEncoding(Box<Expr>),  // Buffer.isEncoding(encoding) -> boolean
+    BufferConcatWithLength {
+        // Buffer.concat(list, totalLength) -> Buffer
+        list: Box<Expr>,
+        total_length: Box<Expr>,
+    },
+    BufferIsBuffer(Box<Expr>),   // Buffer.isBuffer(obj) -> boolean
+    BufferIsEncoding(Box<Expr>), // Buffer.isEncoding(encoding) -> boolean
     BufferByteLength {
         data: Box<Expr>,
         encoding: Option<Box<Expr>>,
diff --git a/crates/perry-hir/src/lower/expr_call/array_only_methods.rs b/crates/perry-hir/src/lower/expr_call/array_only_methods.rs
index ecae2a548..f49e847bd 100644
--- a/crates/perry-hir/src/lower/expr_call/array_only_methods.rs
+++ b/crates/perry-hir/src/lower/expr_call/array_only_methods.rs
@@ -463,6 +463,7 @@ pub(super) fn try_array_only_methods(
                         if matches!(
                             &array_expr,
                             Expr::BufferConcat(_)
+                                | Expr::BufferConcatWithLength { .. }
                                 | Expr::BufferFrom { .. }
                                 | Expr::BufferSlice { .. }
                         ) {
diff --git a/crates/perry-hir/src/lower/expr_call/module_static.rs b/crates/perry-hir/src/lower/expr_call/module_static.rs
index addd0847c..db9f9c248 100644
--- a/crates/perry-hir/src/lower/expr_call/module_static.rs
+++ b/crates/perry-hir/src/lower/expr_call/module_static.rs
@@ -1038,9 +1038,15 @@ pub(super) fn try_module_static_methods(
                         }
                         "concat" => {
                             if !args.is_empty() {
-                                return Ok(Ok(Expr::BufferConcat(Box::new(
-                                    args.into_iter().next().unwrap(),
-                                ))));
+                                let mut args_iter = args.into_iter();
+                                let list = args_iter.next().unwrap();
+                                if let Some(total_length) = args_iter.next() {
+                                    return Ok(Ok(Expr::BufferConcatWithLength {
+                                        list: Box::new(list),
+                                        total_length: Box::new(total_length),
+                                    }));
+                                }
+                                return Ok(Ok(Expr::BufferConcat(Box::new(list))));
                             }
                         }
                         "of" => {
diff --git a/crates/perry-hir/src/lower/expr_call/native_module.rs b/crates/perry-hir/src/lower/expr_call/native_module.rs
index 35cf1102e..2c7ad355e 100644
--- a/crates/perry-hir/src/lower/expr_call/native_module.rs
+++ b/crates/perry-hir/src/lower/expr_call/native_module.rs
@@ -462,6 +462,12 @@ pub(super) fn try_native_module_methods(
                         }
                         "concat" => {
                             let list = args.first().cloned().unwrap_or(Expr::Array(vec![]));
+                            if let Some(total_length) = args.get(1).cloned() {
+                                return Ok(Ok(Expr::BufferConcatWithLength {
+                                    list: Box::new(list),
+                                    total_length: Box::new(total_length),
+                                }));
+                            }
                             return Ok(Ok(Expr::BufferConcat(Box::new(list))));
                         }
                         "of" => {
diff --git a/crates/perry-hir/src/lower/expr_call/url_date_instance.rs b/crates/perry-hir/src/lower/expr_call/url_date_instance.rs
index 323087deb..f0eb75a33 100644
--- a/crates/perry-hir/src/lower/expr_call/url_date_instance.rs
+++ b/crates/perry-hir/src/lower/expr_call/url_date_instance.rs
@@ -133,6 +133,7 @@ pub(super) fn try_url_date_weakref_instance(
                         | Expr::BufferAlloc { .. }
                         | Expr::BufferAllocUnsafe(_)
                         | Expr::BufferConcat(_)
+                        | Expr::BufferConcatWithLength { .. }
                 ) {
                     return Ok(Ok(Expr::Call {
                         callee: Box::new(Expr::PropertyGet {
diff --git a/crates/perry-hir/src/stable_hash/expr.rs b/crates/perry-hir/src/stable_hash/expr.rs
index 475f2287e..5a523df2b 100644
--- a/crates/perry-hir/src/stable_hash/expr.rs
+++ b/crates/perry-hir/src/stable_hash/expr.rs
@@ -274,6 +274,7 @@ impl SH for Expr {
             Expr::BufferAlloc { size, fill, encoding } => { tag(h, 216); size.as_ref().hash(h); fill.hash(h); encoding.hash(h); }
             Expr::BufferAllocUnsafe(e) => { tag(h, 217); e.as_ref().hash(h); }
             Expr::BufferConcat(e) => { tag(h, 218); e.as_ref().hash(h); }
+            Expr::BufferConcatWithLength { list, total_length } => { tag(h, 11222); list.as_ref().hash(h); total_length.as_ref().hash(h); }
             Expr::BufferIsBuffer(e) => { tag(h, 219); e.as_ref().hash(h); }
             Expr::BufferIsEncoding(e) => { tag(h, 11219); e.as_ref().hash(h); }
             Expr::BufferByteLength { data, encoding } => { tag(h, 220); data.as_ref().hash(h); encoding.hash(h); }
diff --git a/crates/perry-hir/src/walker/expr_mut.rs b/crates/perry-hir/src/walker/expr_mut.rs
index 71232f3d3..176fc98dd 100644
--- a/crates/perry-hir/src/walker/expr_mut.rs
+++ b/crates/perry-hir/src/walker/expr_mut.rs
@@ -307,6 +307,10 @@ where
         | Expr::TemplateRaw(v) => {
             f(v);
         }
+        Expr::BufferConcatWithLength { list, total_length } => {
+            f(list);
+            f(total_length);
+        }
 
         Expr::UrlCanParseWithBase { input, base } => {
             f(input);
diff --git a/crates/perry-hir/src/walker/expr_ref.rs b/crates/perry-hir/src/walker/expr_ref.rs
index 1ed231a0e..6945da8ca 100644
--- a/crates/perry-hir/src/walker/expr_ref.rs
+++ b/crates/perry-hir/src/walker/expr_ref.rs
@@ -308,6 +308,10 @@ where
         | Expr::TemplateRaw(v) => {
             f(v);
         }
+        Expr::BufferConcatWithLength { list, total_length } => {
+            f(list);
+            f(total_length);
+        }
 
         Expr::UrlCanParseWithBase { input, base } => {
             f(input);
diff --git a/crates/perry-runtime/src/buffer/from.rs b/crates/perry-runtime/src/buffer/from.rs
index 0f4132dde..2b3b77d7b 100644
--- a/crates/perry-runtime/src/buffer/from.rs
+++ b/crates/perry-runtime/src/buffer/from.rs
@@ -853,9 +853,53 @@ pub extern "C" fn js_buffer_alloc_unsafe(size: i32) -> *mut BufferHeader {
     buf
 }
 
-/// Concatenate multiple buffers
-#[no_mangle]
-pub extern "C" fn js_buffer_concat(arr_ptr: *const ArrayHeader) -> *mut BufferHeader {
+fn throw_buffer_concat_invalid_arg_type(index: usize) -> ! {
+    static REGISTER_TYPE_ERROR: std::sync::Once = std::sync::Once::new();
+    REGISTER_TYPE_ERROR.call_once(|| {
+        crate::object::js_register_class_extends_error(crate::error::CLASS_ID_TYPE_ERROR);
+    });
+
+    let obj = crate::object::js_object_alloc(crate::error::CLASS_ID_TYPE_ERROR, 4);
+    unsafe {
+        let set = |key: &[u8], value: f64| {
+            let key_ptr = crate::string::js_string_from_bytes(key.as_ptr(), key.len() as u32);
+            crate::object::js_object_set_field_by_name(obj, key_ptr, value);
+        };
+        let str_val = |s: &[u8]| -> f64 {
+            let ptr = crate::string::js_string_from_bytes(s.as_ptr(), s.len() as u32);
+            f64::from_bits(crate::JSValue::string_ptr(ptr).bits())
+        };
+        let message =
+            format!("The \"list[{index}]\" argument must be an instance of Buffer or Uint8Array");
+        set(b"name", str_val(b"TypeError"));
+        set(b"code", str_val(b"ERR_INVALID_ARG_TYPE"));
+        set(b"message", str_val(message.as_bytes()));
+    }
+    crate::exception::js_throw(crate::value::js_nanbox_pointer(obj as i64))
+}
+
+fn normalize_buffer_concat_total_length(total_length: f64) -> Option<usize> {
+    let jsval = crate::JSValue::from_bits(total_length.to_bits());
+    if jsval.is_undefined() {
+        return None;
+    }
+    if jsval.is_int32() {
+        return Some((jsval.as_int32().max(0)) as usize);
+    }
+    if jsval.is_bool() {
+        return Some(if jsval.as_bool() { 1 } else { 0 });
+    }
+    if jsval.is_null() || total_length.is_nan() || !total_length.is_finite() || total_length <= 0.0
+    {
+        return Some(0);
+    }
+    Some((total_length.trunc() as usize).min(u32::MAX as usize))
+}
+
+fn js_buffer_concat_impl(
+    arr_ptr: *const ArrayHeader,
+    requested_total_length: Option<usize>,
+) -> *mut BufferHeader {
     // Strip NaN-boxing tags if present
     let arr_ptr = {
         let bits = arr_ptr as u64;
@@ -884,34 +928,55 @@ pub extern "C" fn js_buffer_concat(arr_ptr: *const ArrayHeader) -> *mut BufferHe
             }
         };
 
-        // Calculate total size
-        let mut total_size: usize = 0;
+        let mut actual_total_size: usize = 0;
         for i in 0..len {
             let raw_bits = strip_nanbox((*arr_data.add(i)).to_bits());
-            let buf_ptr = raw_bits as *const BufferHeader;
-            if !buf_ptr.is_null() && raw_bits >= 0x1000 {
-                total_size += (*buf_ptr).length as usize;
+            if raw_bits < 0x1000 || !is_registered_buffer(raw_bits as usize) {
+                throw_buffer_concat_invalid_arg_type(i);
             }
+            let buf_ptr = raw_bits as *const BufferHeader;
+            actual_total_size = actual_total_size.saturating_add((*buf_ptr).length as usize);
         }
+        let total_size = requested_total_length.unwrap_or(actual_total_size);
+        let total_size = total_size.min(u32::MAX as usize);
 
         // Allocate result buffer
         let result = buffer_alloc(total_size as u32);
         (*result).length = total_size as u32;
+        ptr::write_bytes(buffer_data_mut(result), 0, total_size);
 
         // Copy data
         let mut offset: usize = 0;
         for i in 0..len {
             let raw_bits = strip_nanbox((*arr_data.add(i)).to_bits());
             let buf_ptr = raw_bits as *const BufferHeader;
-            if !buf_ptr.is_null() && raw_bits >= 0x1000 {
-                let buf_len = (*buf_ptr).length as usize;
-                let src_data = buffer_data(buf_ptr);
-                let dst_data = buffer_data_mut(result).add(offset);
-                ptr::copy_nonoverlapping(src_data, dst_data, buf_len);
-                offset += buf_len;
+            let buf_len = (*buf_ptr).length as usize;
+            let remaining = total_size.saturating_sub(offset);
+            if remaining == 0 {
+                break;
             }
+            let copy_len = buf_len.min(remaining);
+            let src_data = buffer_data(buf_ptr);
+            let dst_data = buffer_data_mut(result).add(offset);
+            ptr::copy_nonoverlapping(src_data, dst_data, copy_len);
+            offset += copy_len;
         }
 
         result
     }
 }
+
+/// Concatenate multiple buffers.
+#[no_mangle]
+pub extern "C" fn js_buffer_concat(arr_ptr: *const ArrayHeader) -> *mut BufferHeader {
+    js_buffer_concat_impl(arr_ptr, None)
+}
+
+/// Concatenate multiple buffers using Node's optional totalLength semantics.
+#[no_mangle]
+pub extern "C" fn js_buffer_concat_with_length(
+    arr_ptr: *const ArrayHeader,
+    total_length: f64,
+) -> *mut BufferHeader {
+    js_buffer_concat_impl(arr_ptr, normalize_buffer_concat_total_length(total_length))
+}
diff --git a/crates/perry-runtime/src/buffer/mod.rs b/crates/perry-runtime/src/buffer/mod.rs
index ba1c09b17..6b9712933 100644
--- a/crates/perry-runtime/src/buffer/mod.rs
+++ b/crates/perry-runtime/src/buffer/mod.rs
@@ -38,8 +38,9 @@ pub use header::{
 // ---- Re-exports: Buffer.from / alloc / concat (FFI) ----
 pub use from::{
     js_array_buffer_new, js_buffer_alloc, js_buffer_alloc_fill_value, js_buffer_alloc_unsafe,
-    js_buffer_concat, js_buffer_fill, js_buffer_fill_range, js_buffer_fill_value_range,
-    js_buffer_from_array, js_buffer_from_arraybuffer_slice, js_buffer_from_string,
+    js_buffer_concat, js_buffer_concat_with_length, js_buffer_fill, js_buffer_fill_range,
+    js_buffer_fill_value_range, js_buffer_from_array, js_buffer_from_arraybuffer_slice,
+    js_buffer_from_string,
     js_buffer_from_value, js_data_view_new, js_encoding_tag_from_value, js_shared_array_buffer_new,
     js_uint8array_alloc, js_uint8array_from_array, js_uint8array_new,
 };
diff --git a/crates/perry-runtime/src/object/native_module_dispatch.rs b/crates/perry-runtime/src/object/native_module_dispatch.rs
index dd11ad195..3c51bd5e9 100644
--- a/crates/perry-runtime/src/object/native_module_dispatch.rs
+++ b/crates/perry-runtime/src/object/native_module_dispatch.rs
@@ -283,7 +283,12 @@ pub(crate) unsafe fn dispatch_native_module_method(
         }
         ("buffer.Buffer", "concat") => {
             let arr = ptr_addr(arg(0)) as *const crate::array::ArrayHeader;
-            ptr_to_f64(crate::buffer::js_buffer_concat(arr) as *const u8)
+            let buf = if args_len >= 2 {
+                crate::buffer::js_buffer_concat_with_length(arr, arg(1))
+            } else {
+                crate::buffer::js_buffer_concat(arr)
+            };
+            ptr_to_f64(buf as *const u8)
         }
         ("buffer.Buffer", "of") => {
             let arr = pack_args();