diff --git a/Misc/NEWS.d/next/Library/2026-08-04-19-50-52.gh-issue-150942.B8ytes.rst b/Misc/NEWS.d/next/Library/2026-08-04-19-50-52.gh-issue-150942.B8ytes.rst
new file mode 100644
index 000000000000000..bdc93872f012616
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-04-19-50-52.gh-issue-150942.B8ytes.rst
@@ -0,0 +1,2 @@
+Improve the performance of :meth:`~io.IOBase.readlines` for
+:class:`io.BytesIO`, particularly in free-threaded builds.
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index 7d6053d85cd9e4a..fa3778c12273ca5 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -1,5 +1,6 @@
 #include "Python.h"
 #include "pycore_critical_section.h"  // Py_BEGIN_CRITICAL_SECTION()
+#include "pycore_list.h"              // _PyList_AppendTakeRef()
 #include "pycore_object.h"
 #include "pycore_pyatomic_ft_wrappers.h"
 #include "pycore_sysmodule.h"         // _PySys_GetSizeOf()
@@ -663,11 +664,9 @@ _io_BytesIO_readlines_impl(bytesio *self, PyObject *arg)
         line = PyBytes_FromStringAndSize(output, n);
         if (!line)
             goto on_error;
-        if (PyList_Append(result, line) == -1) {
-            Py_DECREF(line);
+        if (_PyList_AppendTakeRef((PyListObject *)result, line) < 0) {
             goto on_error;
         }
-        Py_DECREF(line);
         size += n;
         if (maxsize > 0 && size >= maxsize)
             break;