diff --git a/crates/vm/src/builtins/bytearray.rs b/crates/vm/src/builtins/bytearray.rs
index c463489df61..fc046460b70 100644
--- a/crates/vm/src/builtins/bytearray.rs
+++ b/crates/vm/src/builtins/bytearray.rs
@@ -1,6 +1,6 @@
 //! Implementation of the python bytearray object.
 use super::{
-    PositionIterInternal, PyBytes, PyDictRef, PyGenericAlias, PyStrRef, PyTuple, PyTupleRef,
+    PositionIterInternal, PyBytes, PyDictRef, PyGenericAlias, PyInt, PyStrRef, PyTuple, PyTupleRef,
     PyType, PyTypeRef, iter::builtins_iter, locked_next,
 };
 use crate::{
@@ -12,7 +12,7 @@ use crate::{
     bytes_inner::{
         ByteInnerFindOptions, ByteInnerHexOptions, ByteInnerNewOptions, ByteInnerPaddingOptions,
         ByteInnerReplaceOptions, ByteInnerSplitOptions, ByteInnerStripOptions, ByteInnerSub,
-        ByteInnerTranslateOptions, BytesJoin, DecodeArgs, PyBytesInner, bytes_decode,
+        ByteInnerTranslateOptions, ByteOr, BytesJoin, DecodeArgs, PyBytesInner, bytes_decode,
     },
     class::PyClassImpl,
     common::{
@@ -317,6 +317,21 @@ impl PyByteArray {
     }
 
     fn __contains__(&self, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult<bool> {
+        // Exact builtins cannot call Python while preparing the needle. The
+        // read lock alone protects their search; a temporary export would make
+        // a concurrent resize fail instead of waiting for that lock.
+        if let Some(bytes) = needle.downcast_ref_if_exact::<PyBytes>(vm) {
+            return Ok(self.borrow_buf().contains_str(bytes.as_bytes()));
+        }
+        let int = if needle.class().is(vm.ctx.types.bool_type) {
+            needle.downcast_ref::<PyInt>()
+        } else {
+            needle.downcast_ref_if_exact::<PyInt>(vm)
+        };
+        if let Some(int) = int {
+            let byte = int.as_bigint().byte_or(vm)?;
+            return Ok(self.borrow_buf().contains(&byte));
+        }
         // Converting the needle runs Python, which must not resize this bytearray.
         self.exports.fetch_add(1, Ordering::Release);
         scopeguard::defer! { self.exports.fetch_sub(1, Ordering::Release); }
diff --git a/extra_tests/snippets/builtin_bytearray.py b/extra_tests/snippets/builtin_bytearray.py
index 2f2793a76cf..1ea800b64db 100644
--- a/extra_tests/snippets/builtin_bytearray.py
+++ b/extra_tests/snippets/builtin_bytearray.py
@@ -1504,3 +1504,86 @@ def __index__(self):
 
 
 test_bytearray_callback_exports()
+
+
+def test_bytearray_contains_builtin_and_callback_exports():
+    for value in (b"", b"a", b"ab\x00\xff", b"\x01"):
+        target = bytearray(value)
+        for needle in (
+            b"",
+            b"a",
+            b"ab",
+            b"z",
+            b"\x00",
+            b"\xff",
+            0,
+            97,
+            255,
+            False,
+            True,
+        ):
+            assert (needle in target) == (needle in value)
+        assert target in target
+
+    def must_raise_buffer_error(action):
+        try:
+            action()
+        except BufferError:
+            return
+        raise AssertionError("resize was not rejected")
+
+    target = bytearray(b"a")
+    view = memoryview(target)
+    try:
+        assert b"a" in target
+        assert 97 in target
+        must_raise_buffer_error(lambda: target.append(0))
+        target[:] = b"b"
+        assert b"b" in target
+        assert 98 in target
+    finally:
+        view.release()
+    target.append(0)
+    assert target == b"b\x00"
+
+    class IndexNeedle:
+        def __index__(self):
+            must_raise_buffer_error(lambda: target.append(0))
+            target[0] = 98
+            return 98
+
+    class BytesNeedle(bytes):
+        __index__ = IndexNeedle.__index__
+
+    for needle in (IndexNeedle(), BytesNeedle(b"\xdd")):
+        target[:] = b"a"
+        assert needle in target
+        assert target == b"b"
+        target.append(0)
+        assert target == b"b\x00"
+
+    for needle in (-1, 256):
+        with assert_raises(ValueError):
+            needle in target
+
+    events = [0, 0]
+
+    class BufferNeedle:
+        def __buffer__(self, flags):
+            must_raise_buffer_error(lambda: target.append(0))
+            target[0] = 98
+            events[0] += 1
+            return memoryview(b"b")
+
+        def __release_buffer__(self, view):
+            must_raise_buffer_error(lambda: target.append(0))
+            events[1] += 1
+
+    target[:] = b"a"
+    assert BufferNeedle() in target
+    assert events == [1, 1]
+    target.append(0)
+    assert target == b"b\x00"
+
+
+test_bytearray_contains_builtin_and_callback_exports()