diff --git a/builtin/builtin.mbti b/builtin/builtin.mbti
index 0926ef1e9..8cd2a0610 100644
--- a/builtin/builtin.mbti
+++ b/builtin/builtin.mbti
@@ -535,6 +535,7 @@ fn[A] FixedArray::unsafe_blit(Self[A], Int, Self[A], Int, Int) -> Unit
 fn[T] FixedArray::unsafe_get(Self[T], Int) -> T
 fn[T] FixedArray::unsafe_set(Self[T], Int, T) -> Unit
 
+#deprecated
 fn Bytes::copy(Bytes) -> Bytes
 fn Bytes::length(Bytes) -> Int
 fn Bytes::make(Int, Byte) -> Bytes
diff --git a/builtin/bytes.mbt b/builtin/bytes.mbt
index 20c73538d..dccb660af 100644
--- a/builtin/bytes.mbt
+++ b/builtin/bytes.mbt
@@ -176,21 +176,7 @@ pub fn FixedArray::blit_from_bytes(
 }
 
 ///|
-/// Creates a new byte sequence by copying all bytes from the input sequence.
-///
-/// Parameters:
-///
-/// * `bytes` : The byte sequence to be copied.
-///
-/// Returns a new `Bytes` containing the same sequence of bytes as the input.
-///
-/// Example:
-///
-/// ```moonbit
-///   let original = b"\x01\x02\x03"
-///   let copy = original.copy()
-///   inspect(copy, content="b\"\\x01\\x02\\x03\"")
-/// ```
+#deprecated("Bytes are immutable. Use `FixedArray::blit_from_bytes` if it's really necessary.")
 pub fn Bytes::copy(self : Bytes) -> Bytes {
   Bytes::makei(self.length(), fn(i) { self[i] })
 }
diff --git a/builtin/bytes_test.mbt b/builtin/bytes_test.mbt
index 1dc528caa..04b4e3656 100644
--- a/builtin/bytes_test.mbt
+++ b/builtin/bytes_test.mbt
@@ -33,12 +33,6 @@ test "blit_from_string" {
   assert_eq(@bytes.from_fixedarray(bytes).to_unchecked_string(), str)
 }
 
-///|
-test "copy" {
-  let copy_bytes = HELLO_WORLD.copy()
-  assert_eq(copy_bytes.to_unchecked_string(), HELLO_WORLD.to_unchecked_string())
-}
-
 ///|
 test "set_utf8_char (ASCII)" {
   let arr = FixedArray::makei(4, _ => b'\x00')
@@ -149,7 +143,9 @@ test "set_utf16be_char" {
 
 ///|
 test "op_equal" {
-  let copy_bytes = HELLO_WORLD.copy()
+  let copy_bytes = FixedArray::make(HELLO_WORLD.length(), Byte::default())
+  copy_bytes.blit_from_bytes(0, HELLO_WORLD, 0, HELLO_WORLD.length())
+  let copy_bytes = Bytes::from_fixedarray(copy_bytes)
   assert_eq(HELLO_WORLD, copy_bytes)
   assert_not_eq(HELLO_WORLD, Bytes::new(10))
 }